How can I login with multiple social services with Firebase?

Question

I want users to be able to authenticate to my Firebase application using multiple different auth providers, such as Facebook, Twitter, or Github. Once authenticated, I want

Answer 1

I know this post exists for months but when I faced this problem, it took lot of my time to make the code more flexible. Base on Andrew code above, I tweaked the code a little.

Sample data store:

userMappings
|---facebook:777
|   |---user:"123"
|---twitter:888
    |---user:"123"
users
|---123
    |---userMappings
        |---facebook: "facebook:777"
        |---twitter: "twitter:888"

Security rules:

"userMappings": {
  "$login_id": {
    ".read": "$login_id === auth.uid",
    ".write": "auth!== null && (data.val() === null || $login_id === auth.uid)"
  }
},

"users": {
  "$user_id": {
    ".read": "data.child('userMappings/'+auth.provider).val()===auth.uid",
    ".write": "auth!= null && (data.val() === null || data.child('userMappings/'+auth.provider).val()===auth.uid)"
  }
}

So userMappings is still the first information we look up when login by Facebook, Twitter.... the userMappings' user will point to the main account in users. So after login by Facebook or Twitter, we can look up the main user account. In users we keep list of userMapping that can access to its data.

When create new user, we have to create an account in users first. The id for user in users could be anything we want. This is flexible because we can provide more login method like Google, Github without adding more security rule.