Admin: Allow for the consistent filtering of `auth_redirect_scheme`

Merge of [37651] to the 4.1 branch.

See #37047.

Built from https://develop.svn.wordpress.org/branches/4.1@37762


git-svn-id: http://core.svn.wordpress.org/branches/4.1@37727 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/pluggable.php

@@ -1007,18 +1007,14 @@ function auth_redirect() {
 		}
 	}
 
-	if ( is_user_admin() ) {
-		$scheme = 'logged_in';
-	} else {
 	/**
-		 * Filter the authentication redirect scheme.
+	 * Filters the authentication redirect scheme.
 	 *
 	 * @since 2.9.0
 	 *
 	 * @param string $scheme Authentication redirect scheme. Default empty.
 	 */
 	$scheme = apply_filters( 'auth_redirect_scheme', '' );
-	}
 
 	if ( $user_id = wp_validate_auth_cookie( '',  $scheme) ) {
 		/**