Merge a8f76b0b7b into 42e1829b37

alts/src/main/java/io/grpc/alts/JwtTokenFileCallCredentials.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2025 The gRPC Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc.alts;
+
+import com.google.api.client.json.gson.GsonFactory;
+import com.google.api.client.json.webtoken.JsonWebSignature;
+import com.google.auth.oauth2.AccessToken;
+import com.google.auth.oauth2.OAuth2Credentials;
+import com.google.common.io.Files;
+import io.grpc.CallCredentials;
+import io.grpc.auth.MoreCallCredentials;
+import java.io.File;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.util.Date;
+
+/**
+ * JWT token file call credentials.
+ * See gRFC A97 (https://github.com/grpc/proposal/pull/492).
+ */
+public final class JwtTokenFileCallCredentials extends OAuth2Credentials {
+  private String path = null;
+
+  private JwtTokenFileCallCredentials(String path) {
+    this.path = path;
+  }
+
+  @Override
+  public AccessToken refreshAccessToken() throws IOException {
+    String tokenString = new String(Files.toByteArray(new File(path)), StandardCharsets.UTF_8);
+    Long expTime = JsonWebSignature.parse(new GsonFactory(), tokenString)
+        .getPayload()
+        .getExpirationTimeSeconds();
+    if (expTime == null) {
+      throw new IOException("No expiration time found for JWT token");
+    }
+
+    return AccessToken.newBuilder()
+        .setTokenValue(tokenString)
+        .setExpirationTime(new Date(expTime * 1000L))
+        .build();
+  }
+
+  // using {@link MoreCallCredentials} adapter to be compatible with {@link CallCredentials} iface
+  public static CallCredentials create(String path) {
+    JwtTokenFileCallCredentials jwtTokenFileCallCredentials = new JwtTokenFileCallCredentials(path);
+    return MoreCallCredentials.from(jwtTokenFileCallCredentials);
+  }
+}

alts/src/test/java/io/grpc/alts/JwtTokenFileCallCredentialsTest.java

@@ -0,0 +1,122 @@
+/*
+ * Copyright 2025 The gRPC Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc.alts;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
+
+import com.google.auth.oauth2.AccessToken;
+import com.google.common.io.BaseEncoding;
+import com.google.common.truth.Truth;
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.lang.reflect.Constructor;
+import java.nio.charset.StandardCharsets;
+import java.util.Date;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Unit tests for {@link JwtTokenFileCallCredentials}. */
+@RunWith(JUnit4.class)
+public class JwtTokenFileCallCredentialsTest {
+  @Rule
+  public TemporaryFolder tempFolder = new TemporaryFolder();
+
+  private File jwtTokenFile;
+  private JwtTokenFileCallCredentials unit;
+
+  @Before
+  public void setUp() throws Exception {
+    jwtTokenFile = tempFolder.newFile(new String("jwt.json"));
+
+    Constructor<JwtTokenFileCallCredentials> ctor =
+        JwtTokenFileCallCredentials.class.getDeclaredConstructor(String.class);
+    ctor.setAccessible(true);
+    unit = ctor.newInstance(jwtTokenFile.toString());
+  }
+
+  private void fillJwtTokenWithoutExpiration(File jwtFile) throws Exception {
+    FileOutputStream outputStream = new FileOutputStream(jwtFile);
+    String content =
+        BaseEncoding.base64().encode(
+            new String("{\"typ\": \"JWT\", \"alg\": \"HS256\"}").getBytes(StandardCharsets.UTF_8))
+        + "."
+        + BaseEncoding.base64().encode(
+            new String("{\"name\": \"Google\"}").getBytes(StandardCharsets.UTF_8))
+        + "."
+        + BaseEncoding.base64().encode(new String("signature").getBytes(StandardCharsets.UTF_8));
+    outputStream.write(content.getBytes(StandardCharsets.UTF_8));
+    outputStream.close();
+  }
+
+  private String fillValidJwtToken(File jwtFile, Long expTime) throws Exception {
+    FileOutputStream outputStream = new FileOutputStream(jwtFile);
+    String content =
+        BaseEncoding.base64().encode(
+            new String("{\"typ\": \"JWT\", \"alg\": \"HS256\"}").getBytes(StandardCharsets.UTF_8))
+        + "."
+        + BaseEncoding.base64().encode(
+            String.format("{\"exp\": %d}", expTime).getBytes(StandardCharsets.UTF_8))
+        + "."
+        + BaseEncoding.base64().encode(new String("signature").getBytes(StandardCharsets.UTF_8));
+    outputStream.write(content.getBytes(StandardCharsets.UTF_8));
+    outputStream.close();
+    return content;
+  }
+
+  @Test
+  public void givenJwtTokenFileEmpty_WhenTokenRefreshed_ExpectException() {
+    assertThrows(IllegalArgumentException.class, () -> {
+      unit.refreshAccessToken();
+    });
+  }
+
+  @Test
+  public void givenJwtTokenFileWithoutExpiration_WhenTokenRefreshed_ExpectException()
+      throws Exception {
+
+    fillJwtTokenWithoutExpiration(jwtTokenFile);
+
+    Exception ex = assertThrows(IOException.class, () -> {
+      unit.refreshAccessToken();
+    });
+
+    String expectedMsg = "No expiration time found for JWT token";
+    String actualMsg = ex.getMessage();
+
+    assertEquals(expectedMsg, actualMsg);
+  }
+
+  @Test
+  public void givenValidJwtTokenFile_WhenTokenRefreshed_ExpectAccessTokenInstance()
+      throws Exception {
+    final Long givenExpTimeInSeconds = 1753364000L;
+    final Date givenExpTimeDate = new Date(givenExpTimeInSeconds * 1000L);
+
+    String givenTokenValue = fillValidJwtToken(jwtTokenFile, givenExpTimeInSeconds);
+
+    AccessToken token = unit.refreshAccessToken();
+
+    Truth.assertThat(token.getExpirationTime()).isEquivalentAccordingToCompareTo(givenExpTimeDate);
+    assertEquals(token.getTokenValue(), givenTokenValue);
+  }
+}

xds/src/main/java/io/grpc/xds/GrpcBootstrapperImpl.java

@@ -18,7 +18,10 @@ package io.grpc.xds;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableMap;
+import io.grpc.CallCredentials;
 import io.grpc.ChannelCredentials;
+import io.grpc.CompositeCallCredentials;
+import io.grpc.internal.GrpcUtil;
 import io.grpc.internal.JsonUtil;
 import io.grpc.xds.client.BootstrapperImpl;
 import io.grpc.xds.client.XdsInitializationException;
@@ -33,6 +36,8 @@ class GrpcBootstrapperImpl extends BootstrapperImpl {
   private static final String BOOTSTRAP_PATH_SYS_PROPERTY = "io.grpc.xds.bootstrap";
   private static final String BOOTSTRAP_CONFIG_SYS_ENV_VAR = "GRPC_XDS_BOOTSTRAP_CONFIG";
   private static final String BOOTSTRAP_CONFIG_SYS_PROPERTY = "io.grpc.xds.bootstrapConfig";
+  private static final String GRPC_EXPERIMENTAL_XDS_BOOTSTRAP_CALL_CREDS =
+      "GRPC_EXPERIMENTAL_XDS_BOOTSTRAP_CALL_CREDS";
   @VisibleForTesting
   String bootstrapPathFromEnvVar = System.getenv(BOOTSTRAP_PATH_SYS_ENV_VAR);
   @VisibleForTesting
@@ -41,6 +46,9 @@ class GrpcBootstrapperImpl extends BootstrapperImpl {
   String bootstrapConfigFromEnvVar = System.getenv(BOOTSTRAP_CONFIG_SYS_ENV_VAR);
   @VisibleForTesting
   String bootstrapConfigFromSysProp = System.getProperty(BOOTSTRAP_CONFIG_SYS_PROPERTY);
+  @VisibleForTesting
+  static boolean xdsBootstrapCallCredsEnabled = GrpcUtil.getFlag(
+      GRPC_EXPERIMENTAL_XDS_BOOTSTRAP_CALL_CREDS, false);
 
   GrpcBootstrapperImpl() {
     super();
@@ -90,7 +98,7 @@ class GrpcBootstrapperImpl extends BootstrapperImpl {
   }
 
   @Override
-  protected Object getImplSpecificConfig(Map<String, ?> serverConfig, String serverUri)
+  protected Object getImplSpecificChannelCredConfig(Map<String, ?> serverConfig, String serverUri)
       throws XdsInitializationException {
     return getChannelCredentials(serverConfig, serverUri);
   }
@@ -135,4 +143,58 @@ class GrpcBootstrapperImpl extends BootstrapperImpl {
     }
     return null;
   }
+
+  @Override
+  protected Object getImplSpecificCallCredConfig(Map<String, ?> serverConfig, String serverUri)
+      throws XdsInitializationException {
+    return getCallCredentials(serverConfig, serverUri);
+  }
+
+  private static CallCredentials getCallCredentials(Map<String, ?> serverConfig,
+                                                    String serverUri)
+      throws XdsInitializationException {
+    List<?> rawCallCredsList = JsonUtil.getList(serverConfig, "call_creds");
+    if (rawCallCredsList == null || rawCallCredsList.isEmpty()) {
+      return null;
+    }
+    CallCredentials callCredentials =
+        parseCallCredentials(JsonUtil.checkObjectList(rawCallCredsList), serverUri);
+    return callCredentials;
+  }
+
+  @Nullable
+  private static CallCredentials parseCallCredentials(List<Map<String, ?>> jsonList,
+                                                      String serverUri)
+      throws XdsInitializationException {
+    CallCredentials callCredentials = null;
+    if (xdsBootstrapCallCredsEnabled) {
+      for (Map<String, ?> callCreds : jsonList) {
+        String type = JsonUtil.getString(callCreds, "type");
+        if (type != null) {
+          XdsCredentialsProvider provider =  XdsCredentialsRegistry.getDefaultRegistry()
+              .getProvider(type);
+          if (provider != null) {
+            Map<String, ?> config = JsonUtil.getObject(callCreds, "config");
+            if (config == null) {
+              config = ImmutableMap.of();
+            }
+            CallCredentials parsedCallCredentials = provider.newCallCredentials(config);
+            if (parsedCallCredentials == null) {
+              throw new XdsInitializationException(
+                  "Invalid bootstrap: server " + serverUri + " with invalid 'config' for " + type
+                  + " 'call_creds'");
+            }
+
+            if (callCredentials == null) {
+              callCredentials = parsedCallCredentials;
+            } else {
+              callCredentials = new CompositeCallCredentials(
+                  callCredentials, parsedCallCredentials);
+            }
+          }
+        }
+      }
+    }
+    return callCredentials;
+  }
 }

xds/src/main/java/io/grpc/xds/GrpcXdsTransportFactory.java

@@ -23,6 +23,8 @@ import io.grpc.CallCredentials;
 import io.grpc.CallOptions;
 import io.grpc.ChannelCredentials;
 import io.grpc.ClientCall;
+import io.grpc.CompositeCallCredentials;
+import io.grpc.CompositeChannelCredentials;
 import io.grpc.Context;
 import io.grpc.Grpc;
 import io.grpc.ManagedChannel;
@@ -68,12 +70,27 @@ final class GrpcXdsTransportFactory implements XdsTransportFactory {
 
     public GrpcXdsTransport(Bootstrapper.ServerInfo serverInfo, CallCredentials callCredentials) {
       String target = serverInfo.target();
-      ChannelCredentials channelCredentials = (ChannelCredentials) serverInfo.implSpecificConfig();
+      ChannelCredentials channelCredentials =
+          (ChannelCredentials) serverInfo.implSpecificChannelCredConfig();
+      Object callCredConfig = serverInfo.implSpecificCallCredConfig();
+      if (callCredConfig != null) {
+        channelCredentials = CompositeChannelCredentials.create(
+          channelCredentials, (CallCredentials) callCredConfig);
+      }
+
       this.channel = Grpc.newChannelBuilder(target, channelCredentials)
           .keepAliveTime(5, TimeUnit.MINUTES)
           .build();
+
+      if (callCredentials != null && callCredConfig != null) {
+        this.callCredentials =
+            new CompositeCallCredentials(callCredentials, (CallCredentials) callCredConfig);
+      } else if (callCredConfig != null) {
+        this.callCredentials = (CallCredentials) callCredConfig;
+      } else {
         this.callCredentials = callCredentials;
       }
+    }
 
     @VisibleForTesting
     public GrpcXdsTransport(ManagedChannel channel, CallCredentials callCredentials) {

xds/src/main/java/io/grpc/xds/XdsCredentialsProvider.java

@@ -16,6 +16,7 @@
 
 package io.grpc.xds;
 
+import io.grpc.CallCredentials;
 import io.grpc.ChannelCredentials;
 import io.grpc.Internal;
 import java.util.Map;
@@ -49,6 +50,17 @@ public abstract class XdsCredentialsProvider {
   */
   protected abstract ChannelCredentials newChannelCredentials(Map<String, ?> jsonConfig);
 
+  /**
+  * Creates a {@link CallCredentials} from the given jsonConfig, or
+  * {@code null} if the given config is invalid. The provider is free to ignore
+  * the config if it's not needed for producing the channel credentials.
+  *
+  * @param jsonConfig json config that can be consumed by the provider to create
+  *                   the channel credentials
+  *
+  */
+  protected abstract CallCredentials newCallCredentials(Map<String, ?> jsonConfig);
+
   /**
    * Returns the xDS credential name associated with this provider which makes it selectable
    * via {@link XdsCredentialsRegistry#getProvider}. This is called only when the class is loaded.

xds/src/main/java/io/grpc/xds/XdsCredentialsRegistry.java

@@ -114,7 +114,7 @@ final class XdsCredentialsRegistry {
               new XdsCredentialsProviderPriorityAccessor());
       if (providerList.isEmpty()) {
         logger.warning("No XdsCredsRegistry found via ServiceLoader, including for GoogleDefault, "
-            + "TLS and Insecure. This is probably due to a broken build.");
+            + "TLS, Insecure and JWT token file. This is probably due to a broken build.");
       }
       instance = new XdsCredentialsRegistry();
       for (XdsCredentialsProvider provider : providerList) {
@@ -171,6 +171,12 @@ final class XdsCredentialsRegistry {
       logger.log(Level.WARNING, "Unable to find TlsXdsCredentialsProvider", e);
     }
 
+    try {
+      list.add(Class.forName("io.grpc.xds.internal.JwtTokenFileXdsCredentialsProvider"));
+    } catch (ClassNotFoundException e) {
+      logger.log(Level.WARNING, "Unable to find JwtTokenFileXdsCredentialsProvider", e);
+    }
+
     return Collections.unmodifiableList(list);
   }
 

xds/src/main/java/io/grpc/xds/client/Bootstrapper.java

@@ -57,22 +57,50 @@ public abstract class Bootstrapper {
   public abstract static class ServerInfo {
     public abstract String target();
 
-    public abstract Object implSpecificConfig();
+    public abstract Object implSpecificChannelCredConfig();
+
+    @Nullable public abstract Object implSpecificCallCredConfig();
 
     public abstract boolean ignoreResourceDeletion();
 
     public abstract boolean isTrustedXdsServer();
 
     @VisibleForTesting
-    public static ServerInfo create(String target, @Nullable Object implSpecificConfig) {
-      return new AutoValue_Bootstrapper_ServerInfo(target, implSpecificConfig, false, false);
+    public static ServerInfo create(
+        String target,
+        @Nullable Object implSpecificChannelCredConfig) {
+      return new AutoValue_Bootstrapper_ServerInfo(
+          target,
+          implSpecificChannelCredConfig,
+          null,
+          false,
+          false);
     }
   
     @VisibleForTesting
     public static ServerInfo create(
-        String target, Object implSpecificConfig, boolean ignoreResourceDeletion,
+        String target,
+        @Nullable Object implSpecificChannelCredConfig,
+        @Nullable Object implSpecificCallCredConfig) {
+      return new AutoValue_Bootstrapper_ServerInfo(
+          target,
+          implSpecificChannelCredConfig,
+          implSpecificCallCredConfig,
+          false,
+          false);
+    }
+
+    @VisibleForTesting
+    public static ServerInfo create(
+        String target,
+        Object implSpecificChannelCredConfig,
+        @Nullable Object implSpecificCallCredConfig,
+        boolean ignoreResourceDeletion,
         boolean isTrustedXdsServer) {
-      return new AutoValue_Bootstrapper_ServerInfo(target, implSpecificConfig,
+      return new AutoValue_Bootstrapper_ServerInfo(
+          target,
+          implSpecificChannelCredConfig,
+          implSpecificCallCredConfig,
           ignoreResourceDeletion, isTrustedXdsServer);
     }
   }

xds/src/main/java/io/grpc/xds/client/BootstrapperImpl.java

@@ -68,9 +68,13 @@ public abstract class BootstrapperImpl extends Bootstrapper {
 
   protected abstract String getJsonContent() throws IOException, XdsInitializationException;
 
-  protected abstract Object getImplSpecificConfig(Map<String, ?> serverConfig, String serverUri)
+  protected abstract Object getImplSpecificChannelCredConfig(
+      Map<String, ?> serverConfig, String serverUri)
       throws XdsInitializationException;
 
+  protected abstract Object getImplSpecificCallCredConfig(
+      Map<String, ?> serverConfig, String serverUri)
+      throws XdsInitializationException;
 
   /**
    * Reads and parses bootstrap config. The config is expected to be in JSON format.
@@ -245,7 +249,9 @@ public abstract class BootstrapperImpl extends Bootstrapper {
       }
       logger.log(XdsLogLevel.INFO, "xDS server URI: {0}", serverUri);
 
-      Object implSpecificConfig = getImplSpecificConfig(serverConfig, serverUri);
+      Object implSpecificChannelCredConfig =
+          getImplSpecificChannelCredConfig(serverConfig, serverUri);
+      Object implSpecificCallCredConfig = getImplSpecificCallCredConfig(serverConfig, serverUri);
 
       boolean ignoreResourceDeletion = false;
       // "For forward compatibility reasons, the client will ignore any entry in the list that it
@@ -256,7 +262,11 @@ public abstract class BootstrapperImpl extends Bootstrapper {
         ignoreResourceDeletion = serverFeatures.contains(SERVER_FEATURE_IGNORE_RESOURCE_DELETION);
       }
       servers.add(
-          ServerInfo.create(serverUri, implSpecificConfig, ignoreResourceDeletion,
+          ServerInfo.create(
+            serverUri,
+            implSpecificChannelCredConfig,
+            implSpecificCallCredConfig,
+            ignoreResourceDeletion,
             serverFeatures != null
                 && serverFeatures.contains(SERVER_FEATURE_TRUSTED_XDS_SERVER)));
     }

xds/src/main/java/io/grpc/xds/internal/GoogleDefaultXdsCredentialsProvider.java

@@ -16,6 +16,7 @@
 
 package io.grpc.xds.internal;
 
+import io.grpc.CallCredentials;
 import io.grpc.ChannelCredentials;
 import io.grpc.alts.GoogleDefaultChannelCredentials;
 import io.grpc.xds.XdsCredentialsProvider;
@@ -33,6 +34,11 @@ public final class GoogleDefaultXdsCredentialsProvider extends XdsCredentialsPro
     return GoogleDefaultChannelCredentials.create();
   }
 
+  @Override
+  protected CallCredentials newCallCredentials(Map<String, ?> jsonConfig) {
+    return null;
+  }
+
   @Override
   protected String getName() {
     return CREDS_NAME;

xds/src/main/java/io/grpc/xds/internal/InsecureXdsCredentialsProvider.java

@@ -16,6 +16,7 @@
 
 package io.grpc.xds.internal;
 
+import io.grpc.CallCredentials;
 import io.grpc.ChannelCredentials;
 import io.grpc.InsecureChannelCredentials;
 import io.grpc.xds.XdsCredentialsProvider;
@@ -33,6 +34,11 @@ public final class InsecureXdsCredentialsProvider extends XdsCredentialsProvider
     return InsecureChannelCredentials.create();
   }
 
+  @Override
+  protected CallCredentials newCallCredentials(Map<String, ?> jsonConfig) {
+    return null;
+  }
+
   @Override
   protected String getName() {
     return CREDS_NAME;

xds/src/main/java/io/grpc/xds/internal/JwtTokenFileXdsCredentialsProvider.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2025 The gRPC Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc.xds.internal;
+
+import io.grpc.CallCredentials;
+import io.grpc.ChannelCredentials;
+import io.grpc.alts.JwtTokenFileCallCredentials;
+import io.grpc.internal.JsonUtil;
+import io.grpc.xds.XdsCredentialsProvider;
+import java.io.File;
+import java.util.Map;
+
+/**
+ * A wrapper class that supports {@link JwtTokenFileXdsCredentialsProvider} for
+ * Xds by implementing {@link XdsCredentialsProvider}.
+ */
+public class JwtTokenFileXdsCredentialsProvider extends XdsCredentialsProvider {
+  private static final String CREDS_NAME = "jwt_token_file";
+
+  @Override
+  protected ChannelCredentials newChannelCredentials(Map<String, ?> jsonConfig) {
+    return null;
+  }
+
+  @Override
+  protected CallCredentials newCallCredentials(Map<String, ?> jsonConfig) {
+    if (jsonConfig == null) {
+      return null;
+    }
+
+    String jwtTokenPath = JsonUtil.getString(jsonConfig, getName());
+    if (jwtTokenPath == null || !new File(jwtTokenPath).isFile()) {
+      return null;
+    }
+
+    return JwtTokenFileCallCredentials.create(jwtTokenPath);
+  }
+
+  @Override
+  protected String getName() {
+    return CREDS_NAME;
+  }
+
+  @Override
+  public boolean isAvailable() {
+    return true;
+  }
+
+  @Override
+  public int priority() {
+    return 5;
+  }
+
+}

xds/src/main/java/io/grpc/xds/internal/TlsXdsCredentialsProvider.java

@@ -16,6 +16,7 @@
 
 package io.grpc.xds.internal;
 
+import io.grpc.CallCredentials;
 import io.grpc.ChannelCredentials;
 import io.grpc.TlsChannelCredentials;
 import io.grpc.xds.XdsCredentialsProvider;
@@ -33,6 +34,11 @@ public final class TlsXdsCredentialsProvider extends XdsCredentialsProvider {
     return TlsChannelCredentials.create();
   }
 
+  @Override
+  protected CallCredentials newCallCredentials(Map<String, ?> jsonConfig) {
+    return null;
+  }
+
   @Override
   protected String getName() {
     return CREDS_NAME;

xds/src/main/resources/META-INF/services/io.grpc.xds.XdsCredentialsProvider

@@ -1,3 +1,4 @@
 io.grpc.xds.internal.GoogleDefaultXdsCredentialsProvider
 io.grpc.xds.internal.InsecureXdsCredentialsProvider
+io.grpc.xds.internal.JwtTokenFileXdsCredentialsProvider
 io.grpc.xds.internal.TlsXdsCredentialsProvider

xds/src/test/java/io/grpc/xds/GrpcBootstrapperImplTest.java

@@ -17,6 +17,9 @@
 package io.grpc.xds;
 
 import static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.fail;
 import static org.mockito.Mockito.mock;
@@ -24,6 +27,7 @@ import static org.mockito.Mockito.verifyNoInteractions;
 
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Iterables;
+import io.grpc.CompositeCallCredentials;
 import io.grpc.InsecureChannelCredentials;
 import io.grpc.TlsChannelCredentials;
 import io.grpc.internal.GrpcUtil;
@@ -37,13 +41,16 @@ import io.grpc.xds.client.CommonBootstrapperTestUtils;
 import io.grpc.xds.client.EnvoyProtoData.Node;
 import io.grpc.xds.client.Locality;
 import io.grpc.xds.client.XdsInitializationException;
+import java.io.File;
 import java.io.IOException;
 import java.util.List;
 import java.util.Map;
 import org.junit.After;
 import org.junit.Assert;
 import org.junit.Before;
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
 
@@ -60,11 +67,16 @@ public class GrpcBootstrapperImplTest {
   private String originalBootstrapConfigFromEnvVar;
   private String originalBootstrapConfigFromSysProp;
   private boolean originalExperimentalXdsFallbackFlag;
+  private boolean originalExperimentalXdsBootstrapCallCredsFlag;
+
+  @Rule
+  public TemporaryFolder tempFolder = new TemporaryFolder();
 
   @Before
   public void setUp() {
     saveEnvironment();
     originalExperimentalXdsFallbackFlag = CommonBootstrapperTestUtils.setEnableXdsFallback(true);
+    GrpcBootstrapperImpl.xdsBootstrapCallCredsEnabled = true;
     bootstrapper.bootstrapPathFromEnvVar = BOOTSTRAP_FILE_PATH;
   }
 
@@ -73,6 +85,8 @@ public class GrpcBootstrapperImplTest {
     originalBootstrapPathFromSysProp = bootstrapper.bootstrapPathFromSysProp;
     originalBootstrapConfigFromEnvVar = bootstrapper.bootstrapConfigFromEnvVar;
     originalBootstrapConfigFromSysProp = bootstrapper.bootstrapConfigFromSysProp;
+    originalExperimentalXdsBootstrapCallCredsFlag =
+        GrpcBootstrapperImpl.xdsBootstrapCallCredsEnabled;
   }
 
   @After
@@ -82,6 +96,8 @@ public class GrpcBootstrapperImplTest {
     bootstrapper.bootstrapConfigFromEnvVar = originalBootstrapConfigFromEnvVar;
     bootstrapper.bootstrapConfigFromSysProp = originalBootstrapConfigFromSysProp;
     CommonBootstrapperTestUtils.setEnableXdsFallback(originalExperimentalXdsFallbackFlag);
+    GrpcBootstrapperImpl.xdsBootstrapCallCredsEnabled =
+        originalExperimentalXdsBootstrapCallCredsFlag;
   }
 
   @Test
@@ -115,7 +131,9 @@ public class GrpcBootstrapperImplTest {
     assertThat(info.servers()).hasSize(1);
     ServerInfo serverInfo = Iterables.getOnlyElement(info.servers());
     assertThat(serverInfo.target()).isEqualTo(SERVER_URI);
-    assertThat(serverInfo.implSpecificConfig()).isInstanceOf(InsecureChannelCredentials.class);
+    assertThat(serverInfo.implSpecificChannelCredConfig()).isInstanceOf(
+        InsecureChannelCredentials.class);
+    assertNull(serverInfo.implSpecificCallCredConfig());
     assertThat(info.node()).isEqualTo(
         getNodeBuilder()
             .setId("ENVOY_NODE_ID")
@@ -168,12 +186,14 @@ public class GrpcBootstrapperImplTest {
     List<ServerInfo> serverInfoList = info.servers();
     assertThat(serverInfoList.get(0).target())
         .isEqualTo("trafficdirector-foo.googleapis.com:443");
-    assertThat(serverInfoList.get(0).implSpecificConfig())
+    assertThat(serverInfoList.get(0).implSpecificChannelCredConfig())
         .isInstanceOf(TlsChannelCredentials.class);
+    assertNull(serverInfoList.get(0).implSpecificCallCredConfig());
     assertThat(serverInfoList.get(1).target())
         .isEqualTo("trafficdirector-bar.googleapis.com:443");
-    assertThat(serverInfoList.get(1).implSpecificConfig())
+    assertThat(serverInfoList.get(1).implSpecificChannelCredConfig())
         .isInstanceOf(InsecureChannelCredentials.class);
+    assertNull(serverInfoList.get(0).implSpecificCallCredConfig());
     assertThat(info.node()).isEqualTo(
         getNodeBuilder()
             .setId("ENVOY_NODE_ID")
@@ -217,7 +237,9 @@ public class GrpcBootstrapperImplTest {
     assertThat(info.servers()).hasSize(1);
     ServerInfo serverInfo = Iterables.getOnlyElement(info.servers());
     assertThat(serverInfo.target()).isEqualTo(SERVER_URI);
-    assertThat(serverInfo.implSpecificConfig()).isInstanceOf(InsecureChannelCredentials.class);
+    assertThat(serverInfo.implSpecificChannelCredConfig()).isInstanceOf(
+        InsecureChannelCredentials.class);
+    assertNull(serverInfo.implSpecificCallCredConfig());
     assertThat(info.node()).isEqualTo(
         getNodeBuilder()
             .setId("ENVOY_NODE_ID")
@@ -288,7 +310,9 @@ public class GrpcBootstrapperImplTest {
     assertThat(info.servers()).hasSize(1);
     ServerInfo serverInfo = Iterables.getOnlyElement(info.servers());
     assertThat(serverInfo.target()).isEqualTo(SERVER_URI);
-    assertThat(serverInfo.implSpecificConfig()).isInstanceOf(InsecureChannelCredentials.class);
+    assertThat(serverInfo.implSpecificChannelCredConfig()).isInstanceOf(
+        InsecureChannelCredentials.class);
+    assertNull(serverInfo.implSpecificCallCredConfig());
     assertThat(info.node()).isEqualTo(getNodeBuilder().build());
   }
 
@@ -583,7 +607,9 @@ public class GrpcBootstrapperImplTest {
     BootstrapInfo info = bootstrapper.bootstrap();
     ServerInfo serverInfo = Iterables.getOnlyElement(info.servers());
     assertThat(serverInfo.target()).isEqualTo(SERVER_URI);
-    assertThat(serverInfo.implSpecificConfig()).isInstanceOf(InsecureChannelCredentials.class);
+    assertThat(serverInfo.implSpecificChannelCredConfig()).isInstanceOf(
+        InsecureChannelCredentials.class);
+    assertNull(serverInfo.implSpecificCallCredConfig());
     assertThat(serverInfo.ignoreResourceDeletion()).isFalse();
   }
 
@@ -605,7 +631,9 @@ public class GrpcBootstrapperImplTest {
     BootstrapInfo info = bootstrapper.bootstrap();
     ServerInfo serverInfo = Iterables.getOnlyElement(info.servers());
     assertThat(serverInfo.target()).isEqualTo(SERVER_URI);
-    assertThat(serverInfo.implSpecificConfig()).isInstanceOf(InsecureChannelCredentials.class);
+    assertThat(serverInfo.implSpecificChannelCredConfig()).isInstanceOf(
+        InsecureChannelCredentials.class);
+    assertNull(serverInfo.implSpecificCallCredConfig());
     assertThat(serverInfo.ignoreResourceDeletion()).isFalse();
   }
 
@@ -627,7 +655,9 @@ public class GrpcBootstrapperImplTest {
     BootstrapInfo info = bootstrapper.bootstrap();
     ServerInfo serverInfo = Iterables.getOnlyElement(info.servers());
     assertThat(serverInfo.target()).isEqualTo(SERVER_URI);
-    assertThat(serverInfo.implSpecificConfig()).isInstanceOf(InsecureChannelCredentials.class);
+    assertThat(serverInfo.implSpecificChannelCredConfig()).isInstanceOf(
+        InsecureChannelCredentials.class);
+    assertNull(serverInfo.implSpecificCallCredConfig());
     // Only ignore_resource_deletion feature enabled: confirm it's on, and xds_v3 is off.
     assertThat(serverInfo.ignoreResourceDeletion()).isTrue();
   }
@@ -650,7 +680,9 @@ public class GrpcBootstrapperImplTest {
     BootstrapInfo info = bootstrapper.bootstrap();
     ServerInfo serverInfo = Iterables.getOnlyElement(info.servers());
     assertThat(serverInfo.target()).isEqualTo(SERVER_URI);
-    assertThat(serverInfo.implSpecificConfig()).isInstanceOf(InsecureChannelCredentials.class);
+    assertThat(serverInfo.implSpecificChannelCredConfig()).isInstanceOf(
+        InsecureChannelCredentials.class);
+    assertNull(serverInfo.implSpecificCallCredConfig());
     assertThat(serverInfo.isTrustedXdsServer()).isTrue();
   }
 
@@ -672,7 +704,9 @@ public class GrpcBootstrapperImplTest {
     BootstrapInfo info = bootstrapper.bootstrap();
     ServerInfo serverInfo = Iterables.getOnlyElement(info.servers());
     assertThat(serverInfo.target()).isEqualTo(SERVER_URI);
-    assertThat(serverInfo.implSpecificConfig()).isInstanceOf(InsecureChannelCredentials.class);
+    assertThat(serverInfo.implSpecificChannelCredConfig()).isInstanceOf(
+        InsecureChannelCredentials.class);
+    assertNull(serverInfo.implSpecificCallCredConfig());
     // ignore_resource_deletion features enabled: confirm both are on.
     assertThat(serverInfo.ignoreResourceDeletion()).isTrue();
   }
@@ -898,6 +932,131 @@ public class GrpcBootstrapperImplTest {
     }
   }
 
+  @Test
+  public void parseNotSupportedCallCredentials() throws Exception {
+    String rawData = "{\n"
+        + "  \"xds_servers\": [\n"
+        + "    {\n"
+        + "      \"server_uri\": \"" + SERVER_URI + "\",\n"
+        + "      \"channel_creds\": [\n"
+        + "        {\"type\": \"insecure\"}\n"
+        + "      ],\n"
+        + "      \"call_creds\": [\n"
+        + "        {\"type\": \"unknown\"}\n"
+        + "      ]\n"
+        + "    }\n"
+        + "  ]\n"
+        + "}";
+    bootstrapper.setFileReader(createFileReader(BOOTSTRAP_FILE_PATH, rawData));
+    BootstrapInfo info = bootstrapper.bootstrap();
+    assertThat(info.servers()).hasSize(1);
+    ServerInfo serverInfo = Iterables.getOnlyElement(info.servers());
+    assertNull(serverInfo.implSpecificCallCredConfig());
+  }
+
+  @Test
+  public void parseSupportedCallCredentialsWithInvalidConfig() throws Exception {
+    String rawData = "{\n"
+        + "  \"xds_servers\": [\n"
+        + "    {\n"
+        + "      \"server_uri\": \"" + SERVER_URI + "\",\n"
+        + "      \"channel_creds\": [\n"
+        + "        {\"type\": \"insecure\"}\n"
+        + "      ],\n"
+        + "      \"call_creds\": [\n"
+        + "        {\n"
+        + "          \"type\": \"jwt_token_file\",\n"
+        + "          \"config\": {}\n"
+        + "        }\n"
+        + "      ]\n"
+        + "    }\n"
+        + "  ]\n"
+        + "}";
+    bootstrapper.setFileReader(createFileReader(BOOTSTRAP_FILE_PATH, rawData));
+    Exception ex = assertThrows(XdsInitializationException.class, () -> {
+      bootstrapper.bootstrap();
+    });
+
+    String expectedMsg = "Invalid bootstrap: server "
+        + SERVER_URI + " with invalid 'config' for jwt_token_file 'call_creds'";
+    String actualMsg = ex.getMessage();
+
+    assertEquals(expectedMsg, actualMsg);
+  }
+
+  @Test
+  public void parseSupportedCallCredentialsWithJwtFileMissingConfig() throws Exception {
+    String rawData = "{\n"
+        + "  \"xds_servers\": [\n"
+        + "    {\n"
+        + "      \"server_uri\": \"" + SERVER_URI + "\",\n"
+        + "      \"channel_creds\": [\n"
+        + "        {\"type\": \"insecure\"}\n"
+        + "      ],\n"
+        + "      \"call_creds\": [\n"
+        + "        {\n"
+        + "          \"type\": \"jwt_token_file\",\n"
+        + "          \"config\": {\n"
+        + "            \"jwt_token_file\": \"/path/to/file\"\n"
+        + "          }\n"
+        + "        }\n"
+        + "      ]\n"
+        + "    }\n"
+        + "  ]\n"
+        + "}";
+    bootstrapper.setFileReader(createFileReader(BOOTSTRAP_FILE_PATH, rawData));
+    Exception ex = assertThrows(XdsInitializationException.class, () -> {
+      bootstrapper.bootstrap();
+    });
+
+    String expectedMsg = "Invalid bootstrap: server "
+        + SERVER_URI + " with invalid 'config' for jwt_token_file 'call_creds'";
+    String actualMsg = ex.getMessage();
+
+    assertEquals(expectedMsg, actualMsg);
+  }
+
+  @Test
+  public void parseTwoSupportedCallCredentialsWithValidConfig() throws Exception {
+    File jwtToken_1 = tempFolder.newFile(new String("jwt-token-1.txt"));
+    File jwtToken_2 = tempFolder.newFile(new String("jwt-token-2.txt"));
+
+    String rawData = "{\n"
+        + "  \"xds_servers\": [\n"
+        + "    {\n"
+        + "      \"server_uri\": \"" + SERVER_URI + "\",\n"
+        + "      \"channel_creds\": [\n"
+        + "        {\"type\": \"insecure\"}\n"
+        + "      ],\n"
+        + "      \"call_creds\": [\n"
+        + "        {\n"
+        + "          \"type\": \"jwt_token_file\",\n"
+        + "          \"config\": {\n"
+        + "            \"jwt_token_file\": \"" + jwtToken_1.getAbsolutePath() + "\"\n"
+        + "          }\n"
+        + "        },\n"
+        + "        {\n"
+        + "          \"type\": \"jwt_token_file\",\n"
+        + "          \"config\": {\n"
+        + "            \"jwt_token_file\": \"" + jwtToken_2.getAbsolutePath() + "\"\n"
+        + "          }\n"
+        + "        }\n"
+        + "      ]\n"
+        + "    }\n"
+        + "  ]\n"
+        + "}";
+
+    bootstrapper.setFileReader(createFileReader(BOOTSTRAP_FILE_PATH, rawData));
+    BootstrapInfo info = bootstrapper.bootstrap();
+    assertThat(info.servers()).hasSize(1);
+    ServerInfo serverInfo = Iterables.getOnlyElement(info.servers());
+    assertSame(CompositeCallCredentials.class,
+        serverInfo.implSpecificCallCredConfig().getClass());
+
+    jwtToken_1.delete();
+    jwtToken_2.delete();
+  }
+
   private static BootstrapperImpl.FileReader createFileReader(
       final String expectedPath, final String rawData) {
     return new BootstrapperImpl.FileReader() {

xds/src/test/java/io/grpc/xds/GrpcXdsClientImplDataTest.java

@@ -3549,7 +3549,11 @@ public class GrpcXdsClientImplDataTest {
 
   private XdsResourceType.Args getXdsResourceTypeArgs(boolean isTrustedServer) {
     return new XdsResourceType.Args(
-        ServerInfo.create("http://td", "", false, isTrustedServer), "1.0", null, null, null, null
-    );
+        ServerInfo.create("http://td", "", "", false, isTrustedServer),
+        "1.0",
+        null,
+        null,
+        null,
+        null);
   }
 }

xds/src/test/java/io/grpc/xds/GrpcXdsClientImplTestBase.java

@@ -346,7 +346,11 @@ public abstract class GrpcXdsClientImplTestBase {
       }
     };
 
-    xdsServerInfo = ServerInfo.create(SERVER_URI, CHANNEL_CREDENTIALS, ignoreResourceDeletion(),
+    xdsServerInfo = ServerInfo.create(
+        SERVER_URI,
+        CHANNEL_CREDENTIALS,
+        null,
+        ignoreResourceDeletion(),
         true);
     BootstrapInfo bootstrapInfo =
         Bootstrapper.BootstrapInfo.builder()
@@ -4219,8 +4223,12 @@ public abstract class GrpcXdsClientImplTestBase {
 
   private BootstrapInfo buildBootStrap(String serverUri) {
 
-    ServerInfo xdsServerInfo = ServerInfo.create(serverUri, CHANNEL_CREDENTIALS,
-        ignoreResourceDeletion(), true);
+    ServerInfo xdsServerInfo = ServerInfo.create(
+        serverUri,
+        CHANNEL_CREDENTIALS,
+        null,
+        ignoreResourceDeletion(),
+        true);
 
     return Bootstrapper.BootstrapInfo.builder()
         .servers(Collections.singletonList(xdsServerInfo))

xds/src/test/java/io/grpc/xds/XdsClientFallbackTest.java

@@ -347,7 +347,7 @@ public class XdsClientFallbackTest {
       @Override
       public XdsTransport create(Bootstrapper.ServerInfo serverInfo) {
         ChannelCredentials channelCredentials =
-            (ChannelCredentials) serverInfo.implSpecificConfig();
+            (ChannelCredentials) serverInfo.implSpecificChannelCredConfig();
         return new GrpcXdsTransportFactory.GrpcXdsTransport(
             Grpc.newChannelBuilder(serverInfo.target(), channelCredentials)
               .executor(executor)

xds/src/test/java/io/grpc/xds/XdsCredentialsRegistryTest.java

@@ -22,11 +22,13 @@ import static org.junit.Assert.assertSame;
 import static org.junit.Assert.fail;
 
 import com.google.common.collect.ImmutableMap;
+import io.grpc.CallCredentials;
 import io.grpc.ChannelCredentials;
 import io.grpc.xds.XdsCredentialsProvider;
 import io.grpc.xds.XdsCredentialsRegistry;
 import io.grpc.xds.internal.GoogleDefaultXdsCredentialsProvider;
 import io.grpc.xds.internal.InsecureXdsCredentialsProvider;
+import io.grpc.xds.internal.JwtTokenFileXdsCredentialsProvider;
 import io.grpc.xds.internal.TlsXdsCredentialsProvider;
 import java.util.List;
 import java.util.Map;
@@ -136,11 +138,13 @@ public class XdsCredentialsRegistryTest {
   public void defaultRegistry_providers() {
     Map<String, XdsCredentialsProvider> providers =
             XdsCredentialsRegistry.getDefaultRegistry().providers();
-    assertThat(providers).hasSize(3);
+    assertThat(providers).hasSize(4);
     assertThat(providers.get("google_default").getClass())
         .isEqualTo(GoogleDefaultXdsCredentialsProvider.class);
     assertThat(providers.get("insecure").getClass())
         .isEqualTo(InsecureXdsCredentialsProvider.class);
+    assertThat(providers.get("jwt_token_file").getClass())
+        .isEqualTo(JwtTokenFileXdsCredentialsProvider.class);
     assertThat(providers.get("tls").getClass())
         .isEqualTo(TlsXdsCredentialsProvider.class);
   }
@@ -151,6 +155,7 @@ public class XdsCredentialsRegistryTest {
     assertThat(classes).containsExactly(
         GoogleDefaultXdsCredentialsProvider.class,
         InsecureXdsCredentialsProvider.class,
+        JwtTokenFileXdsCredentialsProvider.class,
         TlsXdsCredentialsProvider.class);
   }
 
@@ -195,6 +200,11 @@ public class XdsCredentialsRegistryTest {
     public ChannelCredentials newChannelCredentials(Map<String, ?> config) {
       throw new UnsupportedOperationException();
     }
+
+    @Override
+    public CallCredentials newCallCredentials(Map<String, ?> config) {
+      throw new UnsupportedOperationException();
+    }
   }
 
   private static class SampleChannelCredentials extends ChannelCredentials {

xds/src/test/java/io/grpc/xds/XdsNameResolverTest.java

@@ -368,13 +368,13 @@ public class XdsNameResolverTest {
     String serviceAuthority = "[::FFFF:129.144.52.38]:80";
     bootstrapInfo = BootstrapInfo.builder()
         .servers(ImmutableList.of(ServerInfo.create(
-            "td.googleapis.com", InsecureChannelCredentials.create(), true, true)))
+            "td.googleapis.com", InsecureChannelCredentials.create(), null, true, true)))
         .node(Node.newBuilder().build())
         .authorities(
             ImmutableMap.of(targetAuthority, AuthorityInfo.create(
                 "xdstp://" + targetAuthority + "/envoy.config.listener.v3.Listener/%s?foo=1&bar=2",
                 ImmutableList.of(ServerInfo.create(
-                    "td.googleapis.com", InsecureChannelCredentials.create(), true, true)))))
+                    "td.googleapis.com", InsecureChannelCredentials.create(), null, true, true)))))
         .build();
     expectedLdsResourceName = "xdstp://xds.authority.com/envoy.config.listener.v3.Listener/"
         + "%5B::FFFF:129.144.52.38%5D:80?bar=2&foo=1"; // query param canonified

xds/src/test/java/io/grpc/xds/client/CommonBootstrapperTestUtils.java

@@ -203,7 +203,7 @@ public class CommonBootstrapperTestUtils {
 
     List<ServerInfo> serverInfos = new ArrayList<>();
     for (String uri : serverUris) {
-      serverInfos.add(ServerInfo.create(uri, CHANNEL_CREDENTIALS, false, true));
+      serverInfos.add(ServerInfo.create(uri, CHANNEL_CREDENTIALS, null, false, true));
     }
     EnvoyProtoData.Node node = EnvoyProtoData.Node.newBuilder().setId("node-id").build();
 

xds/src/test/java/io/grpc/xds/internal/GoogleDefaultXdsCredentialsProviderTest.java

@@ -16,6 +16,7 @@
 
 package io.grpc.xds.internal;
 
+import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
@@ -54,4 +55,9 @@ public class GoogleDefaultXdsCredentialsProviderTest {
     assertSame(CompositeChannelCredentials.class,
         provider.newChannelCredentials(null).getClass());
   }
+
+  @Test
+  public void callCredentials() {
+    assertNull(provider.newCallCredentials(null));
+  }
 }

xds/src/test/java/io/grpc/xds/internal/InsecureXdsCredentialsProviderTest.java

@@ -16,6 +16,7 @@
 
 package io.grpc.xds.internal;
 
+import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
@@ -54,4 +55,9 @@ public class InsecureXdsCredentialsProviderTest {
     assertSame(InsecureChannelCredentials.class,
         provider.newChannelCredentials(null).getClass());
   }
+
+  @Test
+  public void callCredentials() {
+    assertNull(provider.newCallCredentials(null));
+  }
 }

xds/src/test/java/io/grpc/xds/internal/JwtTokenFileXdsCredentialsProviderTest.java

@@ -0,0 +1,85 @@
+/*
+ * Copyright 2025 The gRPC Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc.xds.internal;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import com.google.common.collect.ImmutableMap;
+import io.grpc.InternalServiceProviders;
+import io.grpc.xds.XdsCredentialsProvider;
+import java.io.File;
+import java.util.Map;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+
+/** Unit tests for {@link JwtTokenFileXdsCredentialsProvider}. */
+@RunWith(JUnit4.class)
+public class JwtTokenFileXdsCredentialsProviderTest {
+  private JwtTokenFileXdsCredentialsProvider provider = new JwtTokenFileXdsCredentialsProvider();
+
+  @Rule
+  public TemporaryFolder tempFolder = new TemporaryFolder();
+
+  @Test
+  public void provided() {
+    for (XdsCredentialsProvider current
+        : InternalServiceProviders.getCandidatesViaServiceLoader(
+          XdsCredentialsProvider.class, getClass().getClassLoader())) {
+      if (current instanceof JwtTokenFileXdsCredentialsProvider) {
+        return;
+      }
+    }
+    fail("ServiceLoader unable to load JwtTokenFileXdsCredentialsProvider");
+  }
+
+  @Test
+  public void isAvailable() {
+    assertTrue(provider.isAvailable());
+  }
+
+  @Test
+  public void channelCredentials() {
+    assertNull(provider.newChannelCredentials(null));
+  }
+
+  @Test
+  public void callCredentialsWhenNullConfig() {
+    assertNull(provider.newCallCredentials(null));
+  }
+
+  @Test
+  public void callCredentialsWhenWrongConfig() {
+    Map<String, ?> jsonConfig = ImmutableMap.of("jwt_token_file", "/tmp/not-exisiting-file.txt");
+    assertNull(provider.newCallCredentials(jsonConfig));
+  }
+
+  @Test
+  public void callCredentialsWhenExpectedConfig() throws Exception {
+    File createdFile = tempFolder.newFile(new String("existing-file.txt"));
+    Map<String, ?> jsonConfig = ImmutableMap.of("jwt_token_file", createdFile.toString());
+    assertEquals("io.grpc.auth.GoogleAuthLibraryCallCredentials",
+        provider.newCallCredentials(jsonConfig).getClass().getName());
+    createdFile.delete();
+  }
+}

xds/src/test/java/io/grpc/xds/internal/TlsXdsCredentialsProviderTest.java

@@ -16,6 +16,7 @@
 
 package io.grpc.xds.internal;
 
+import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
@@ -54,4 +55,9 @@ public class TlsXdsCredentialsProviderTest {
     assertSame(TlsChannelCredentials.class,
         provider.newChannelCredentials(null).getClass());
   }
+
+  @Test
+  public void callCredentials() {
+    assertNull(provider.newCallCredentials(null));
+  }
 }