Android Teams login fails during ADFS federation with SSL error

Android users are experiencing sign-in failures to Microsoft Teams due to an SSL error during the ADFS federation process. This affects Android OS versions 10-14 and occurs specifically within the Microsoft Teams mobile app. The problem manifests after the account is entered, failing to load the ADFS page correctly and resulting in infinite loading or a blank screen. While the same account functions on PCs, web browsers, and Outlook Web, the issue is isolated to Android mobile apps utilizing WebView. Android logs indicate an "SSL untrusted" error, despite the use of a valid Sectigo-issued certificate. Troubleshooting, including verifying device settings and reinstalling the Teams app, has been unsuccessful, and the problem replicates across various Android devices. The issue points to a possible incomplete certificate chain or network SSL inspection as the likely culprits. The core questions revolve around required certificate configurations on ADFS for mobile authentication, potential impacts of SSL inspection, and official Microsoft recommendations for such scenarios with Android mobile apps. The issue also appears in other Microsoft mobile applications, strengthening the suspicion of a broader problem related to the certificate or network configuration.