[js][auth] add signInWithEmailLink method + tweak isSignInWithEmailLink

lib/modules/auth/index.js

@@ -413,11 +413,28 @@ export default class Auth extends ModuleBase {
   isSignInWithEmailLink(emailLink: string): boolean {
     return (
       typeof emailLink === 'string' &&
-      emailLink.includes('mode=signIn') &&
-      emailLink.includes('oobCode=')
+      (emailLink.includes('mode=signIn') ||
+        emailLink.includes('mode%3DsignIn')) &&
+      (emailLink.includes('oobCode=') || emailLink.includes('oobCode%3D'))
     );
   }
 
+  /**
+   * Asynchronously signs in using an email and sign-in email link.
+   *
+   * @param {string} email The email account to sign in with.
+   * @param {string} emailLink Sign-in email link.
+   * @return {Promise} A promise resolved upon completion
+   */
+  signInWithEmailLink(
+    email: string,
+    emailLink: string
+  ): Promise<UserCredential> {
+    return getNativeModule(this)
+      .signInWithEmailLink(email, emailLink)
+      .then(userCredential => this._setUserCredential(userCredential));
+  }
+
   /**
    * Completes the password reset process, given a confirmation code and new password.
    *