WordPress: Simple sign in function for custom front-end sign in forms.

WordPress Sign In

/**
 * mm_sign_in function.
 * Sign the user in
 * @access public
 * @return User errors or true if successful signon
 */
function mm_sign_in() {
	if(!is_user_logged_in()) {
		if(!empty($_POST)) {
			// verify nonce
			$nonce = $_POST['signin_nonce'];
			if ( ! wp_verify_nonce( $nonce, 'signin_nonce'  ) )
			{
				die();
			}
	
			$credentials = array();
			$credentials['user_login'] = stripslashes($_POST['signin_username']);
			$credentials['user_password'] = stripslashes($_POST['signin_password']);
			if ( isset($_POST['signin_remember']) ) {
				$credentials['remember'] = (bool)stripslashes($_POST['signin_remember']);
			}
			// sign the user in
			$user = wp_signon($credentials, false);
			// prepare response
			if ( is_wp_error($user) ) {
				return $user->errors;
			} else {
				wp_redirect( home_url() );
				exit();
			}
		}
		return false;
	} else {
		// user is logged in already
		wp_redirect( home_url() );
		exit();
	}
	return false;
}