What is the full list of provider id's for firebase.UserInfo.providerId?

The docs say

For example, 'facebook.com', or 'google.com'.

However, is the exhaustive list available somewhere and can I depend on it? Can these id's ever be a variation, like 'facebook' or 'google' (without the .com)?

Context: I am trying to figure out if the signed in user has a social login. So I want to loop through currentUser.providerData and match it against a known list of providerIds.

From the Sign-In Method sub-tab within Authentication found on the Firebase console for any project, you can see a list of available Sign-in providers:

Firebase's documentation doesn't seem to be even across different platforms, but for the iOS Reference docs there is a list of FirebaseAuth Constants that match up with those from the project console dashboard, with the exception of Anonymous provider:

1. EmailAuthProviderID
2. PhoneAuthProviderID
3. GoogleAuthProviderID
4. FacebookAuthProviderID
5. TwitterAuthProviderID
6. GitHubAuthProviderID
7. AppleAuthProviderID
8. YahooAuthProviderID
9. MicrosoftAuthProviderID

After making a new iOS project from scratch and adding this code to the didFinishLaunchingWithOptions method:

FirebaseApp.configure()
print("EmailAuthProviderID: " + EmailAuthProviderID)
print("PhoneAuthProviderID: " + PhoneAuthProviderID)
print("GoogleAuthProviderID: " + GoogleAuthProviderID)
print("FacebookAuthProviderID: " + FacebookAuthProviderID)
print("TwitterAuthProviderID: " + TwitterAuthProviderID)
print("GitHubAuthProviderID: " + GitHubAuthProviderID)
print("AppleAuthProviderID: " + AppleAuthProviderID)
print("YahooAuthProviderID: " + YahooAuthProviderID)
print("MicrosoftAuthProviderID: " + MicrosoftAuthProviderID)

The output I get is:

EmailAuthProviderID: password
PhoneAuthProviderID: phone
GoogleAuthProviderID: google.com
FacebookAuthProviderID: facebook.com
TwitterAuthProviderID: twitter.com
GitHubAuthProviderID: github.com
AppleAuthProviderID: apple.com
YahooAuthProviderID: yahoo.com
MicrosoftAuthProviderID: hotmail.com