private com.google.protobuf.SingleFieldBuilderV3<
            com.google.cloud.tasks.v2beta3.OAuthToken,
            com.google.cloud.tasks.v2beta3.OAuthToken.Builder,
            com.google.cloud.tasks.v2beta3.OAuthTokenOrBuilder>
        getOauthTokenFieldBuilder() {
      if (oauthTokenBuilder_ == null) {
        if (!(authorizationHeaderCase_ == 5)) {
          authorizationHeader_ = com.google.cloud.tasks.v2beta3.OAuthToken.getDefaultInstance();
        }
        oauthTokenBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.cloud.tasks.v2beta3.OAuthToken,
                com.google.cloud.tasks.v2beta3.OAuthToken.Builder,
                com.google.cloud.tasks.v2beta3.OAuthTokenOrBuilder>(
                (com.google.cloud.tasks.v2beta3.OAuthToken) authorizationHeader_,
                getParentForChildren(),
                isClean());
        authorizationHeader_ = null;
      }
      authorizationHeaderCase_ = 5;
      onChanged();
      return oauthTokenBuilder_;
    }
<pre>
If specified, an
[OAuth token](https://developers.google.com/identity/protocols/OAuth2)
will be generated and attached as the `Authorization` header in the HTTP
request.

This type of authorization should generally only be used when calling
Google APIs hosted on *.googleapis.com.
</pre>

<code>.google.cloud.tasks.v2beta3.OAuthToken oauth_token = 5;</code>
java-tasks/proto-google-cloud-tasks-v2beta3/src/main/java/com/google/cloud/tasks/v2beta3/HttpTarget.java