How to use the Firebase refreshToken to reauthenticate?

When you make call from a browser .getIdToken(true) will automatically refresh your token. Make call like this:

firebase.auth().currentUser.getIdToken(/ forceRefresh / true)
  .then(function(idToken) {
    
  }).catch(function(error) {

});

More info here https://firebase.google.com/docs/reference/js/firebase.User#getIdToken

** UPDATE ** this is also now documented in Firebase REST docs under Exchange a refresh token for an ID token section:

https://firebase.google.com/docs/reference/rest/auth/#section-refresh-token

Currently the only way I found to do this is here: https://developers.google.com/identity/toolkit/reference/securetoken/rest/v1/token

You must make an HTTP request:

POST https://securetoken.googleapis.com/v1/token?key=YOUR_KEY

Where YOUR_KEY can be found in the Google developers console > API Manager > Credentials. It's under the API Keys section.

Make sure request body is structured in the following format:

grant_type=refresh_token&refresh_token=REFRESH_TOKEN

Where REFRESH_TOKEN is the refresh token from Firebase user object when they signed in.

You must set the header Content-Type: application/json or you will get errors (e.g. "MISSING_GRANT_TYPE").

The POST call will return a new idToken (used to be called access_token)

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