REST API: Introduce Application Passwords for API authentication.

In WordPress 4.4 the REST API was first introduced. A few releases later in WordPress 4.7, the Content API endpoints were added, paving the way for Gutenberg and countless in-site experiences. In the intervening years, numerous plugins have built on top of the REST API. Many developers shared a common frustration, the lack of external authentication to the REST API.

This commit introduces Application Passwords to allow users to connect to external applications to their WordPress website. Users can generate individual passwords for each application, allowing for easy revocation and activity monitoring. An authorization flow is introduced to make the connection flow simple for users and application developers.

Application Passwords uses Basic Authentication, and by default is only available over an SSL connection.

Props georgestephanis, kasparsd, timothyblynjacobs, afercia, akkspro, andraganescu, arippberger, aristath, austyfrosty, ayesh, batmoo, bradyvercher, brianhenryie, helen, ipstenu, jeffmatson, jeffpaul, joostdevalk, joshlevinson, kadamwhite, kjbenk, koke, michael-arestad, Otto42, pekz0r, salzano, spacedmonkey, valendesigns.
Fixes #42790.


git-svn-id: https://develop.svn.wordpress.org/trunk@49109 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/user.php

@@ -594,3 +594,61 @@ Please click the following link to activate your user account:
 		wp_specialchars_decode( translate_user_role( $role['name'] ) )
 	);
 }
+
+/**
+ * Checks if the Authorize Application Password request is valid.
+ *
+ * @since 5.6.0
+ *
+ * @param array   $request {
+ *     The array of request data. All arguments are optional and may be empty.
+ *
+ *     @type string $app_name    The suggested name of the application.
+ *     @type string $success_url The url the user will be redirected to after approving the application.
+ *     @type string $reject_url  The url the user will be redirected to after rejecting the application.
+ * }
+ * @param WP_User $user The user authorizing the application.
+ * @return true|WP_Error True if the request is valid, a WP_Error object contains errors if not.
+ */
+function wp_is_authorize_application_password_request_valid( $request, $user ) {
+	$error = new WP_Error();
+
+	if ( ! empty( $request['success_url'] ) ) {
+		$scheme = wp_parse_url( $request['success_url'], PHP_URL_SCHEME );
+
+		if ( 'http' === $scheme ) {
+			$error->add(
+				'invalid_redirect_scheme',
+				__( 'The success url must be served over a secure connection.' )
+			);
+		}
+	}
+
+	if ( ! empty( $request['reject_url'] ) ) {
+		$scheme = wp_parse_url( $request['reject_url'], PHP_URL_SCHEME );
+
+		if ( 'http' === $scheme ) {
+			$error->add(
+				'invalid_redirect_scheme',
+				__( 'The rejection url must be served over a secure connection.' )
+			);
+		}
+	}
+
+	/**
+	 * Fires before application password errors are returned.
+	 *
+	 * @since 5.6.0
+	 *
+	 * @param WP_Error $error   The error object.
+	 * @param array    $request The array of request data.
+	 * @param WP_User  $user    The user authorizing the application.
+	 */
+	do_action( 'wp_authorize_application_password_request_errors', $error, $request, $user );
+
+	if ( $error->has_errors() ) {
+		return $error;
+	}
+
+	return true;
+}