Some users are intermittently unable to access the Microsoft 365 suite portal
ID: MO1420954
Issue type: Incident
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Status
Service Degradation
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Impacted services
Microsoft 365 suite
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Details
Title: Some users are intermittently unable to access the Microsoft 365 suite portal
User impact: Users are intermittently unable to access the Microsoft 365 suite portal.
More info: Access eventually times out with an error message stating, "Bad Request - Header Field Too Long. HTTP Error 400. A request field is too long."
Current status: Our investigation into the authorization flow has identified that tokens utilized by OAuthentication contain a "groups" claim which includes group memberships for users attempting to authentication. We suspect that due to the inclusion of group memberships, this may be resulting in the generation of larger than expected headers, resulting in impact. We're working on a fix that would disable or remove the code which requests the groups claim within the token as a potential remediation, and working to confirm a timeline for fix deployment.
Scope of impact: Your organization is affected by this event, and some users are intermittently unable to access the Microsoft 365 suite portal.
Next update by: Friday, July 10, 2026, at 8:30 PM UTC
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