=====================

OkHttp 4.x upgrades our implementation language from Java to Kotlin and keeps everything else the
same. We’ve chosen Kotlin because it gives us powerful new capabilities while integrating closely
with Java.

We spent a lot of time and energy on retaining strict compatibility with OkHttp 3.x. We’re even
keeping the package name the same: `okhttp3`!

There are three kinds of compatibility we’re tracking:

import org.jspecify.annotations.Nullable;

/**
 * Executor ensuring that all Runnables submitted are executed in order, using the provided
 * Executor, and sequentially such that no two will ever be running at the same time.
 *
 * <p>Tasks submitted to {@link #execute(Runnable)} are executed in FIFO order.
 *
 * <p>The execution of tasks is done by one thread as long as there are tasks left in the queue.

          new ExpectedHashCode(
              new byte[] {
                (byte) 0xef, (byte) 0xcd, (byte) 0xab, (byte) 0x89,
                (byte) 0x67, (byte) 0x45, (byte) 0x23,
                    (byte) 0x01, // up to here, same bytes as above
                (byte) 0x01, (byte) 0x02, (byte) 0x03, (byte) 0x04,
                (byte) 0x05, (byte) 0x06, (byte) 0x07, (byte) 0x08
              },
              0x89abcdef,

   * this {@code Joiner} otherwise.
   *
   * @since 20.0
   */
  public MapJoiner withKeyValueSeparator(char keyValueSeparator) {
    return withKeyValueSeparator(String.valueOf(keyValueSeparator));
  }

  /**
   * Returns a {@code MapJoiner} using the given key-value separator, and the same configuration as
   * this {@code Joiner} otherwise.

        // Create new storage with same salt
        SecureCredentialStorage storage2 = new SecureCredentialStorage(masterPassword.clone(), salt);

        try {
            // Should be able to decrypt with same salt and password
            char[] decrypted = storage2.decryptCredentials(encrypted);
            assertArrayEquals(plaintext, decrypted, "Should decrypt correctly with same salt and password");

  }

  /**
   * Creates an ImmutableMap from the first n entries in entryArray. This implementation may replace
   * the entries in entryArray with its own entry objects (though they will have the same key/value
   * contents), and may take ownership of entryArray.
   */
  static <K, V> ImmutableMap<K, V> fromEntryArray(
      int n, @Nullable Entry<K, V>[] entryArray, boolean throwIfDuplicateKeys) {

    for (prefixFlag in prefixFlags) {
      FLAGS[prefixFlag or FLAG_PADDED] = FLAGS[prefixFlag] + "|PADDED"
    }

    FLAGS[FLAG_END_HEADERS] = "END_HEADERS" // Same as END_PUSH_PROMISE.
    FLAGS[FLAG_PRIORITY] = "PRIORITY" // Same as FLAG_COMPRESSED.
    FLAGS[FLAG_END_HEADERS or FLAG_PRIORITY] = "END_HEADERS|PRIORITY" // Only valid on HEADERS.

A single HTTP call may require follow-up requests to be made to handle authentication challenges, redirects, and HTTP-layer timeouts. In such cases multiple connections, requests, and responses may be attempted. Follow-ups are another reason a single call may trigger multiple events of the same type.

   *   {@code List<ListenableFuture<T>> futures = (List) executor.invokeAll(tasks);}
   * </pre>
   *
   * @return A list of {@code ListenableFuture} instances representing the tasks, in the same
   *     sequential order as produced by the iterator for the given task list, each of which has
   *     completed.
   * @throws RejectedExecutionException {@inheritDoc}
   * @throws NullPointerException if any task is null

But Facebook login doesn't support OpenID Connect. It has its own flavor of OAuth2.

### OpenID (not "OpenID Connect") { #openid-not-openid-connect }

There was also an "OpenID" specification. That tried to solve the same thing as **OpenID Connect**, but was not based on OAuth2.

So, it was a complete additional system.

It is not very popular or used nowadays.

## OpenAPI { #openapi }