private abstract static class First<T> {}

  private abstract static class Second<D> extends First<D> {}

  private abstract static class Third<T, D> extends Second<T> {}

  private abstract static class Fourth<T, D> extends Third<D, T> {}

  private static class ConcreteIS extends Fourth<Integer, String> {}

  private static class ConcreteSI extends Fourth<String, Integer> {}

 *    Note that the private key is not a part of the certificate!
 *
 *  * **A signature issued by another certificate's private key.** This mechanism allows a trusted
 *    third-party to endorse a certificate. Third parties should only endorse certificates once
 *    they've confirmed that the owner of the private key is also the owner of the certificate's
 *    other properties.
 *

   * ClosingFuture)} to start this combination.
   *
   * @param <V1> the type returned by the first future
   * @param <V2> the type returned by the second future
   * @param <V3> the type returned by the third future
   */
  public static final class Combiner3<
          V1 extends @Nullable Object, V2 extends @Nullable Object, V3 extends @Nullable Object>
      extends Combiner {
    /**

    assertThat(pool.connectionCount()).isEqualTo(2)
    assertThat(c1.socket().isClosed).isFalse()
    assertThat(c2.socket().isClosed).isFalse()

    // Add a third connection
    val c3 = factory.newConnection(pool, routeC1, 75L)

    // The third connection bounces the first.
    assertThat(pool.closeConnections(100L)).isEqualTo(0L)
    assertThat(pool.connectionCount()).isEqualTo(2)

          documentation, if provided along with the Derivative Works; or,
          within a display generated by the Derivative Works, if and
          wherever such third-party notices normally appear. The contents
          of the NOTICE file are for informational purposes only and
          do not modify the License. You may add Your own attribution

    b) You must cause the files modified to carry prominent notices
    stating that you changed the files and the date of any change.

    c) You must cause the whole of the work to be licensed at no
    charge to all third parties under the terms of this License.

    d) If a facility in the modified Library refers to a function or a
    table of data to be supplied by an application program that uses

Es handelt sich um eine recht umfangreiche Spezifikation, und sie deckt mehrere komplexe Anwendungsfälle ab.

Sie umfasst Möglichkeiten zur Authentifizierung mithilfe eines „Dritten“ („third party“).

Das ist es, was alle diese „Login mit Facebook, Google, Twitter, GitHub“-Systeme unter der Haube verwenden.

### OAuth 1

OAuth2 is a specification that defines several ways to handle authentication and authorization.

It is quite an extensive specification and covers several complex use cases.

It includes ways to authenticate using a "third party".

That's what all the systems with "login with Facebook, Google, Twitter, GitHub" use underneath.

### OAuth 1

          documentation, if provided along with the Derivative Works; or,
          within a display generated by the Derivative Works, if and
          wherever such third-party notices normally appear. The contents
          of the NOTICE file are for informational purposes only and
          do not modify the License. You may add Your own attribution

          documentation, if provided along with the Derivative Works; or,
          within a display generated by the Derivative Works, if and
          wherever such third-party notices normally appear. The contents
          of the NOTICE file are for informational purposes only and
          do not modify the License. You may add Your own attribution