[REQUIRED] Step 1: Describe your environment

• Xcode version: 12.4
• Firebase SDK version: 7.10.0
• Installation method: CocoaPods
• Firebase Component: Auth

[REQUIRED] Step 2: Describe the problem

Steps to reproduce:

there is a problem when we try to signin with a specific tenant and specific provider using OAuthProvider(see code below for a better understand)

in the file FIROAuthProvider.m line 311 where the params are added in the URL, the param tid is missed, and in some cases this param is needed to the correct functionality of the authentication, don't know if it's missed in the other providers, but in this case of the oauth provider is needed with a multi tenant implementation.

something to add is that Android SDK create the url in a right way when we use the tenant id in the same way.

Relevant Code:

let's use this code to perform the signin...

let auth = Auth.auth()
auth.tenantID = "tenant_id"
let provider = OAuthProvider(providerID: "provider_id", auth: auth)

auth.signIn(with: provider, uiDelegate: nil) { authResult, error in
// handle here the result
}