SharePoint External Authentication Sharing

Question

This was working in the past. Not 100% sure when it did stopped working.

We have external sharing set to new and existing guest and restricted by domains.

When sharing a site this creates a guest account and the external guest has access.

We normally don't share the whole site and only file\folder that is needed. this in the past would just prompt the user with a OTP and they would then have access to that file or folder.

Basically what the chart says, but now when sharing a file/folder we are getting access denied. Not sure why this is happening all of sudden.

Answer 1

Dear @Dahabiyeh, Bahlal,

Thank you for posting on Microsoft Q&A forum.

Based on your description, it appears that your concern relates to B2B file sharing and guest access. We want to inform you about an important update from Microsoft regarding authentication for B2B collaboration.

Starting July 2025, Microsoft Entra ID will begin rolling out a new guest authentication experience for B2B collaboration, with full implementation expected by December 2025. Under this update, One-Time Passcodes (OTP) will no longer be used for protecting data. Instead, guest users will sign in using their home organization’s sign-in page, which will enhance usability and reduce confusion during cross-tenant sign-ins.

What does this mean for you?

• Guest users will enter their email on your branded sign-in screen and then be redirected to their home organization’s sign-in page to authenticate.
• This ensures guests see familiar branding and URL endpoints, making the process clearer and more secure.
• After successful authentication, they will return to your organization to complete the sign-in process.

Action Required: No administrative action is required at this time. However, we recommend reviewing your current B2B collaboration configuration to ensure it aligns with this upcoming change. This will help minimize any potential impact and ensure a smooth transition for your external users.

For more details, please refer to the official Microsoft announcement here:

https://admin.microsoft.com/Adminportal/Home?ref=MessageCenter/:/messages/MC1103608

Note: This link is accessible only with an admin account

If you have any questions or need assistance reviewing your configuration, please feel free to reach out.

Thank you for your patience and understanding

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