Authentication: Allow users to log in using their email address.

Introduces `wp_authenticate_email_password()` which is hooked into `authenticate` after `wp_authenticate_username_password()`.

Props Denis-de-Bernardy, ericlewis, vhomenko, MikeHansenMe, swissspidy, ocean90.
Fixes #9568.

git-svn-id: https://develop.svn.wordpress.org/trunk@36617 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/user.php

@@ -173,6 +173,78 @@ function wp_authenticate_username_password($user, $username, $password) {
 	return $user;
 }
 
+/**
+ * Authenticate the user using the email and password.
+ *
+ * @since 4.5.0
+ *
+ * @param WP_User|WP_Error|null $user     WP_User or WP_Error object if a previous
+ *                                        callback failed authentication.
+ * @param string                $email    Email address for authentication.
+ * @param string                $password Password for authentication.
+ * @return WP_User|WP_Error WP_User on success, WP_Error on failure.
+ */
+function wp_authenticate_email_password( $user, $email, $password ) {
+	if ( $user instanceof WP_User ) {
+		return $user;
+	}
+
+	if ( empty( $email ) || empty( $password ) ) {
+		if ( is_wp_error( $user ) ) {
+			return $user;
+		}
+
+		$error = new WP_Error();
+
+		if ( empty( $email ) ) {
+			$error->add( 'empty_username', __( '<strong>ERROR</strong>: The email field is empty.' ) ); // Uses 'empty_username' for back-compat with wp_signon()
+		}
+
+		if ( empty( $password ) ) {
+			$error->add( 'empty_password', __( '<strong>ERROR</strong>: The password field is empty.' ) );
+		}
+
+		return $error;
+	}
+
+	if ( ! is_email( $email ) ) {
+		return $user;
+	}
+
+	$user = get_user_by( 'email', $email );
+
+	if ( ! $user ) {
+		return new WP_Error( 'invalid_email',
+			__( '<strong>ERROR</strong>: Invalid email address.' ) .
+			' <a href="' . wp_lostpassword_url() . '">' .
+			__( 'Lost your password?' ) .
+			'</a>'
+		);
+	}
+
+	/** This filter is documented in wp-includes/user.php */
+	$user = apply_filters( 'wp_authenticate_user', $user, $password );
+
+	if ( is_wp_error( $user ) ) {
+		return $user;
+	}
+
+	if ( ! wp_check_password( $password, $user->user_pass, $user->ID ) ) {
+		return new WP_Error( 'incorrect_password',
+			sprintf(
+				/* translators: %s: email address */
+				__( '<strong>ERROR</strong>: The password you entered for the email address %s is incorrect.' ),
+				'<strong>' . $email . '</strong>'
+			) .
+			' <a href="' . wp_lostpassword_url() . '">' .
+			__( 'Lost your password?' ) .
+			'</a>'
+		);
+	}
+
+	return $user;
+}
+
 /**
  * Authenticate the user using the WordPress auth cookie.
  *