public Builder mergeOauthToken(com.google.cloud.tasks.v2.OAuthToken value) {
      if (oauthTokenBuilder_ == null) {
        if (authorizationHeaderCase_ == 5
            && authorizationHeader_ != com.google.cloud.tasks.v2.OAuthToken.getDefaultInstance()) {
          authorizationHeader_ =
              com.google.cloud.tasks.v2.OAuthToken.newBuilder(
                      (com.google.cloud.tasks.v2.OAuthToken) authorizationHeader_)
                  .mergeFrom(value)
                  .buildPartial();
        } else {
          authorizationHeader_ = value;
        }
        onChanged();
      } else {
        if (authorizationHeaderCase_ == 5) {
          oauthTokenBuilder_.mergeFrom(value);
        } else {
          oauthTokenBuilder_.setMessage(value);
        }
      }
      authorizationHeaderCase_ = 5;
      return this;
    }
<pre>
If specified, an
[OAuth token](https://developers.google.com/identity/protocols/OAuth2)
will be generated and attached as an `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.v2.OAuthToken oauth_token = 5;</code>
java-tasks/proto-google-cloud-tasks-v2/src/main/java/com/google/cloud/tasks/v2/HttpRequest.java