Add serialVersionUID fields to classes implementing ExternalAccountCredentials

Author: jmahonin

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

@@ -73,6 +73,7 @@ public class AwsCredentials extends ExternalAccountCredentials {
  static final String AWS_IMDSV2_SESSION_TOKEN_HEADER = "x-aws-ec2-metadata-token";
  static final String AWS_IMDSV2_SESSION_TOKEN_TTL_HEADER = "x-aws-ec2-metadata-token-ttl-seconds";
  static final String AWS_IMDSV2_SESSION_TOKEN_TTL = "300";
+ private static final long serialVersionUID = -3670131891574618105L;
 
  /**
  * The AWS credential source. Stores data required to retrieve the AWS credential from the AWS
@@ -81,6 +82,7 @@ public class AwsCredentials extends ExternalAccountCredentials {
  static class AwsCredentialSource extends CredentialSource {
 
  private static final String IMDSV2_SESSION_TOKEN_URL_FIELD_NAME = "imdsv2_session_token_url";
+ private static final long serialVersionUID = -4180558200808134436L;
 
  private final String regionUrl;
  private final String url;

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

@@ -63,12 +63,16 @@
  */
 public class IdentityPoolCredentials extends ExternalAccountCredentials {
 
+ private static final long serialVersionUID = 2471046175477275881L;
+
  /**
  * The IdentityPool credential source. Dictates the retrieval method of the external credential,
  * which can either be through a metadata server or a local file.
  */
  static class IdentityPoolCredentialSource extends ExternalAccountCredentials.CredentialSource {
 
+ private static final long serialVersionUID = -745855247050085694L;
+
  enum IdentityPoolCredentialSourceType {
  FILE,
  URL