How to create wrapper REST API for social login in Firebase? - firebase

Question

I'm trying to create a wrapper REST API for Firebase Authentication using cloud functions.
How can I create user or authenticate user on Firebase once I have the Facebook Access token on client (using Facebook SDK)?

Answer 1

If you are using Firebase Functions with HTTP triggers, you can use firebase.js client node.js library to authenticate a user and return the Firbease tokens in your REST API. You would send the Facebook Access token to that HTTP endpoint, sign in the user with signInWithCredential using node.js client library and return the ID token and refresh token.
If you want to use REST API:
curl 'https://www.googleapis.com/identitytoolkit/v3/relyingparty/verifyAssertion?key=[API_KEY]' \
-H 'Content-Type: application/json' \
--data-binary '{"postBody":"access_token=[FACEBOOK_ACCESS_TOKEN]&providerId=[facebook.com]","requestUri":"[http://localhost]","returnIdpCredential":true,"returnSecureToken":true}'
This would return the Firebase ID token and refresh token:
{
"idToken": "[ID_TOKEN]",
"refreshToken": "[REFRESH_TOKEN]",
...
}
This is all you need for a Firebase Auth session.
To construct the user, call the following API with the ID token:
curl 'https://www.googleapis.com/identitytoolkit/v3/relyingparty/getAccountInfo?key=[API_KEY]' \
-H 'Content-Type: application/json' --data-binary '{"idToken":"[FIREBASE_ID_TOKEN]"}'
This would return the user and the data associated:
{
"kind": "identitytoolkit#GetAccountInfoResponse",
"users": [
{
"localId": "ZY1rJK0...",
"email": "user#example.com",
"emailVerified": false,
"displayName": "John Doe",
"providerUserInfo": [
{
"providerId": "password",
"displayName": "John Doe",
"photoUrl": "http://localhost:8080/img1234567890/photo.png",
"federatedId": "user#example.com",
"email": "user#example.com",
"rawId": "user#example.com",
"screenName": "user#example.com"
}
],
"photoUrl": "https://lh5.googleusercontent.com/.../photo.jpg",
"passwordHash": "...",
"passwordUpdatedAt": 1.484124177E12,
"validSince": "1484124177",
"disabled": false,
"lastLoginAt": "1484628946000",
"createdAt": "1484124142000",
"customAuth": false
}
]
}
To refresh the ID token after it expires, use the refresh token returned:
With REST API:
curl 'https://securetoken.googleapis.com/v1/token?key=[API_KEY]' \
-H 'Content-Type: application/x-www-form-urlencoded' \
--data 'grant_type=refresh_token&refresh_token=[REFRESH_TOKEN]'
This would return a new ID token and refresh token:
{
"expires_in": "3600",
"token_type": "Bearer",
"refresh_token": "[REFRESH_TOKEN]",
"id_token": "[ID_TOKEN]",
"user_id": "tRcfmLH7o2XrNELi...",
"project_id": "1234567890"
}
To use this with client library on the backend:
var firebase = require('firebase');
You send the FB access token from the client to your HTTP endpoint and sign-in with it:
var cred = firebase.auth.FacebookAuthProvider.credential(fbAccessToken);
firebase.auth().signInWithCredential(cred).then(function(user) {
// User is obtained here.
// To get refresh token:
// user.refreshToken
// To get ID token:
return user.getIdToken().then(function(idToken) {
// ...
})
}).catch(function(error) {
});