feat: Support transport and binding-enforcement MDS parameters.

oauth2_http/java/com/google/auth/oauth2/ComputeEngineCredentials.java

@@ -122,6 +122,9 @@ public class ComputeEngineCredentials extends GoogleCredentials
 
   private final Collection<String> scopes;
 
+  private final String transport;
+  private final String bindingEnforcement;
+
   private transient HttpTransportFactory transportFactory;
   private transient String serviceAccountEmail;
 
@@ -152,6 +155,8 @@ private ComputeEngineCredentials(ComputeEngineCredentials.Builder builder) {
       scopeList.removeAll(Arrays.asList("", null));
       this.scopes = ImmutableSet.<String>copyOf(scopeList);
     }
+    this.transport = builder.getTransport();
+    this.bindingEnforcement = builder.getBindingEnforcement();
   }
 
   @Override
@@ -191,7 +196,10 @@ public final Collection<String> getScopes() {
   }
 
   /**
-   * If scopes is specified, add "?scopes=comma-separated-list-of-scopes" to the token url.
+   * If scopes is specified, add "?scopes=comma-separated-list-of-scopes" to the token url. If
+   * transport is specified, add "?transport=xyz" to the token url; xyz is one of "alts" or "mtls".
+   * If bindingEnforcement is specified, add "?binding-enforcement=xyz" to the token url; xyz is one
+   * of "iam-policy" or "on".
    *
    * @return token url with the given scopes
    */
@@ -200,6 +208,12 @@ String createTokenUrlWithScopes() {
     if (!scopes.isEmpty()) {
       tokenUrl.set("scopes", Joiner.on(',').join(scopes));
     }
+    if (!transport.isEmpty()) {
+      tokenUrl.set("transport", transport);
+    }
+    if (!bindingEnforcement.isEmpty()) {
+      tokenUrl.set("binding-enforcement", bindingEnforcement);
+    }
     return tokenUrl.toString();
   }
 
@@ -643,6 +657,9 @@ public static class Builder extends GoogleCredentials.Builder {
     private Collection<String> scopes;
     private Collection<String> defaultScopes;
 
+    private String transport = "";
+    private String bindingEnforcement = "";
+
     protected Builder() {
       setRefreshMargin(COMPUTE_REFRESH_MARGIN);
       setExpirationMargin(COMPUTE_EXPIRATION_MARGIN);
@@ -684,6 +701,18 @@ public Builder setQuotaProjectId(String quotaProjectId) {
       return this;
     }
 
+    @CanIgnoreReturnValue
+    public Builder setTransport(String transport) {
+      this.transport = transport;
+      return this;
+    }
+
+    @CanIgnoreReturnValue
+    public Builder setBindingEnforcement(String bindingEnforcement) {
+      this.bindingEnforcement = bindingEnforcement;
+      return this;
+    }
+
     public HttpTransportFactory getHttpTransportFactory() {
       return transportFactory;
     }
@@ -696,6 +725,14 @@ public Collection<String> getDefaultScopes() {
       return defaultScopes;
     }
 
+    public String getTransport() {
+      return transport;
+    }
+
+    public String getBindingEnforcement() {
+      return bindingEnforcement;
+    }
+
     @Override
     public ComputeEngineCredentials build() {
       return new ComputeEngineCredentials(this);

oauth2_http/javatests/com/google/auth/oauth2/ComputeEngineCredentialsTest.java

@@ -190,6 +190,66 @@ public void buildTokenUrlWithScopes_defaultScopes() {
     assertEquals("bar", scopes.toArray()[1]);
   }
 
+  @Test
+  public void buildTokenUrlSoftMtlsBound_mtls_transport() {
+    ComputeEngineCredentials credentials =
+        ComputeEngineCredentials.newBuilder().setTransport("mtls").build();
+    String softBoundTokenUrl = credentials.createTokenUrlWithScopes();
+
+    assertEquals(TOKEN_URL + "?transport=mtls", softBoundTokenUrl);
+  }
+
+  @Test
+  public void buildTokenUrlSoftMtlsBound_iam_enforcement() {
+    ComputeEngineCredentials credentials =
+        ComputeEngineCredentials.newBuilder().setBindingEnforcement("iam-policy").build();
+    String softBoundTokenUrl = credentials.createTokenUrlWithScopes();
+
+    assertEquals(TOKEN_URL + "?binding-enforcement=iam-policy", softBoundTokenUrl);
+  }
+
+  @Test
+  public void buildTokenUrlSoftMtlsBound_mtls_transport_iam_enforcement() {
+    ComputeEngineCredentials credentials =
+        ComputeEngineCredentials.newBuilder()
+            .setTransport("mtls")
+            .setBindingEnforcement("iam-policy")
+            .build();
+    String softBoundTokenUrl = credentials.createTokenUrlWithScopes();
+
+    assertEquals(TOKEN_URL + "?transport=mtls&binding-enforcement=iam-policy", softBoundTokenUrl);
+  }
+
+  @Test
+  public void buildTokenUrlHardMtlsBound_always_enforced() {
+    ComputeEngineCredentials credentials =
+        ComputeEngineCredentials.newBuilder().setBindingEnforcement("on").build();
+    String softBoundTokenUrl = credentials.createTokenUrlWithScopes();
+
+    assertEquals(TOKEN_URL + "?binding-enforcement=on", softBoundTokenUrl);
+  }
+
+  @Test
+  public void buildTokenUrlHardMtlsBound_mtls_transport_always_enforced() {
+    ComputeEngineCredentials credentials =
+        ComputeEngineCredentials.newBuilder()
+            .setTransport("mtls")
+            .setBindingEnforcement("on")
+            .build();
+    String softBoundTokenUrl = credentials.createTokenUrlWithScopes();
+
+    assertEquals(TOKEN_URL + "?transport=mtls&binding-enforcement=on", softBoundTokenUrl);
+  }
+
+  @Test
+  public void buildTokenUrlHardDirectPathBound_alts_transport() {
+    ComputeEngineCredentials credentials =
+        ComputeEngineCredentials.newBuilder().setTransport("alts").build();
+    String softBoundTokenUrl = credentials.createTokenUrlWithScopes();
+
+    assertEquals(TOKEN_URL + "?transport=alts", softBoundTokenUrl);
+  }
+
   @Test
   public void buildScoped_scopesPresent() throws IOException {
     ComputeEngineCredentials credentials =