App Passwords: Only attempt auth if the username and password are set.

Previously, only the username was checked which caused a PHP warning in some server setups, for instance Shibboleth SSO, where the server only populates the `PHP_AUTH_USER` field.

Props MadtownLems, johnbillion, richard.tape, engahmeds3ed.
Fixes #52003.

Built from https://develop.svn.wordpress.org/trunk@49919


git-svn-id: http://core.svn.wordpress.org/trunk@49618 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/user.php

@@ -462,8 +462,8 @@ function wp_validate_application_password( $input_user ) {
 		return $input_user;
 	}
 
-	// Check that we're trying to authenticate
-	if ( ! isset( $_SERVER['PHP_AUTH_USER'] ) ) {
+	// Both $_SERVER['PHP_AUTH_USER'] and $_SERVER['PHP_AUTH_PW'] must be set in order to attempt authentication.
+	if ( ! isset( $_SERVER['PHP_AUTH_USER'], $_SERVER['PHP_AUTH_PW'] ) ) {
 		return $input_user;
 	}
 

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.7-alpha-49918';
+$wp_version = '5.7-alpha-49919';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.