Initial Changes for trust boundary structure without TB enabled check and header value.

# Conflicts:
#	oauth2_http/java/com/google/auth/oauth2/ComputeEngineCredentials.java
#	oauth2_http/java/com/google/auth/oauth2/GoogleCredentials.java
#	oauth2_http/java/com/google/auth/oauth2/ServiceAccountCredentials.java

# Conflicts:
#	oauth2_http/java/com/google/auth/oauth2/ComputeEngineCredentials.java
#	oauth2_http/java/com/google/auth/oauth2/GoogleCredentials.java
#	oauth2_http/java/com/google/auth/oauth2/ImpersonatedCredentials.java
#	oauth2_http/java/com/google/auth/oauth2/OAuth2Credentials.java
#	oauth2_http/java/com/google/auth/oauth2/ServiceAccountCredentials.java
#	oauth2_http/java/com/google/auth/oauth2/TrustBoundary.java

Author: vverman

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

@@ -115,6 +115,7 @@ class DefaultCredentialsProvider {
    */
   final GoogleCredentials getDefaultCredentials(HttpTransportFactory transportFactory)
       throws IOException {
+    LOGGER.log(Level.FINE, "ajbhdabjh");
     synchronized (this) {
       if (cachedCredentials == null) {
         cachedCredentials = getDefaultCredentialsUnsynchronized(transportFactory);

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

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2024, Google LLC
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *    * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *    * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *
+ *    * Neither the name of Google LLC nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package com.google.auth.oauth2;
+
+import com.google.auth.http.HttpTransportFactory;
+
+/**
+ * An interface for credentials that support trust boundaries. This is an experimental feature.
+ */
+public interface TrustBoundaryCredentials {
+
+  /** Returns whether trust boundary is enabled. */
+  boolean isTrustBoundaryEnabled();
+
+  /** Returns the transport factory. */
+  HttpTransportFactory getTransportFactory();
+}