Firebase Auth with Microsoft (Entra AD) - Login not possible - "Unable to process request due to missing initial state"

[KCO-SK]

Description

Environment: Flutter
Android Studio: 2026.1.1 Patch 1
firebase_core: 4.10.0
Firebase iOS SDK version: 12.14.0
Installation method: SPM
Firebase Component: Auth

When logging in to Firebase with Microsofts Entra AD as an authentication service by using FirebaseAuth.instance.signInWithProvider(microsoftProvider) I am able to open the Microsoft login page.
After entering the correct email + password then the following error appears inside the In-App-Browser:
"Unable to process request due to missing initial state. This may happen if browser sessionStorage is inaccessible or accidentally cleared. Some specific scenarios are - 1) Using IDP-Initiated SAML SSO. 2) Using signInWithRedirect in a storage-partitioned browser environment."

The second login-try afterwards always works.
Most likely because the session has a valid Microsoft token after the first try already, so no redirect is necessary anymore.

We already had this topic in #7153 natively in Swift, but it seems to appear more often again, but don't ask me why.
Maybe changes in one of you last Firebase SDK versions?

Reproducing the issue

The problem appears no matter if I set Chrome or Safari as a standard browser in iOS settings.
It happens on real devices (iPhone and iPad, iOS 26.5.1 and others), but not every user is affected. Most users can login without any problems.
I can't determine in what kind of circumstances the problem occurs, but on a device where the problem occurs, it is always reproducible.

Firebase SDK Version

12.14.0

Xcode Version

26.5

Installation Method

Swift Package Manager

Firebase Product(s)

Authentication

Targeted Platforms

iOS

Relevant Log Output

No log output in this context.
The error message appears within a browser frame.

If using Swift Package Manager, the project's Package.resolved

Expand Package.resolved snippet

{
  "pins" : [
    {
      "identity" : "abseil-cpp-binary",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/google/abseil-cpp-binary.git",
      "state" : {
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        "version" : "1.2024072200.0"
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      "identity" : "app-check",
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      "state" : {
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      "state" : {
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      "identity" : "gtm-session-fetcher",
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  "version" : 2
}

[rizafran]

Thanks for reporting. This issue is related to #13084. Also, I'm wondering if you have tried following one of the best practices on the doc?

[KCO-SK]

Dear @rizafran,

the Firebase document which you are referring to seems to be about "signInWithRedirect".

I am talking about "signInWithProvider":

[rizafran]

Thanks for clarifying, @KCO-SK. I've raised this to our engineers to see what we can do here.

[YiHaoHuang]

We’re seeing the same issue with both MicrosoftProvider and OAuthProvider. The behavior is the same: the first login attempt often fails, but the second attempt usually works.

We’re really hoping this can be resolved.

[martin-ideeri]

Seeing the same thing with Microsoft / Entra sign-in via Flutter