Firebase Node.js SDK获取Access与ID Token的疑问及需求

Let me break this down step by step for you:

1. Why getIdToken() returns the same value as user.accessToken & naming confusion #

First off, in Firebase Auth's client-side SDKs (including the Node.js client SDK), the user.accessToken property is actually an alias for the ID Token. The getIdToken() method is the official, recommended way to retrieve this token because it ensures you get a valid, non-expired token (it will automatically refresh the token if it's close to expiring, whereas accessing the property directly might give you a stale value).

As for why it's named getIdToken() instead of getAccessToken: This comes down to Firebase Auth's terminology. The ID Token is a JWT that identifies the user and contains claims about their identity (like UID, email, etc.). While "access token" is a general OAuth term, Firebase uses "ID Token" specifically for this user-identifying JWT. The accessToken property is a legacy holdover or internal alias, but the method name reflects the token's actual purpose clearly.

2. Returning a complete token object to your client #

If you need to send back an object containing the ID Token (which you're referring to as Access Token here), ID Token, Refresh Token, and expiration time, here's how to do it properly (without relying on the internal stsTokenManager):

const signUpUser = async (email, password) => {
  try {
    const userCredential = await auth.signUpWithEmailAndPassword(email, password);
    const user = userCredential.user;

    // Get valid ID Token (auto-refreshes if needed)
    const idToken = await user.getIdToken();
    // Get token details including expiration time
    const idTokenResult = await user.getIdTokenResult();
    // Get refresh token
    const refreshToken = user.refreshToken;

    // Construct the response object
    const tokenResponse = {
      accessToken: idToken, // Since you want to label it as Access Token
      idToken: idToken,
      refreshToken: refreshToken,
      expiresAt: idTokenResult.expirationTime, // Unix timestamp in milliseconds
      expiresIn: idTokenResult.expirationTime - Date.now() // Time remaining in ms
    };

    return tokenResponse;
  } catch (error) {
    console.error("Sign up error:", error);
    throw error;
  }
};

Why avoid user.stsTokenManager? #

The stsTokenManager is an internal implementation detail of Firebase Auth. It's not part of the public API, which means Firebase could change or remove it at any time without warning. Relying on it makes your code brittle and prone to breaking in future SDK updates. Always use the public methods like getIdToken(), getIdTokenResult(), and the refreshToken property instead—these are guaranteed to be supported across SDK versions.

Just to recap: The "access token" you see on the user object is the same as the ID Token, and using getIdToken() is the safe, official way to retrieve it. The method name reflects the token's identity-focused purpose, which is why it's not called getAccessToken().

内容的提问来源于stack exchange，提问作者Stepan Kolomiyets