A redirect URI, or Reply-URL, is where an authorization server sends a user once their app has been successfully authorized and granted an authorization code or access token. We are updating the Reply-URL list in Exchange Online PowerShell. We’ve found that one of the reply URLs in the existing lists is unsafe and we are replacing it with a new Reply-URL list by the end of March 2021.
We have already released a new version of the Exchange Online PowerShell MFA module that uses the new Reply-URL list, and we strongly recommend moving to this newer version of the module as soon as possible.
If you are an admin of an Exchange Online tenant with any of the following configurations, you are affected by this issue:
Admins using a version of MFA PowerShell module/EXO V2 Module earlier than 1.0.1;
Developers / Admins who create automation with ModernAuth using Reply-URL to acquire OAuth token and then invoke a New-PSSession; or
Hybrid customers HCW versions earlier than 17.0.5785.0.
The Reply-URL being deprecated (by the end of March 2021) is ietf:wg:oauth:2.0:oob. The new Reply-URLs that should be used are: