code: public java.lang.String getProviderId() {
      java.lang.Object ref = providerId_;
      if (ref instanceof java.lang.String) {
        return (java.lang.String) ref;
      } else {
        com.google.protobuf.ByteString bs = 
            (com.google.protobuf.ByteString) ref;
        java.lang.String s = bs.toStringUtf8();
        providerId_ = s;
        return s;
      }
    }
docs: <pre>
  [id][google.api.AuthProvider.id] from authentication provider.
  Example:
  provider_id: bookstore_auth
  </pre>
  
  <code>string provider_id = 1;</code>