We developed our own Security Token Service to use claim based authentication on OWA Exchange Server. In our implementation, OWA successfully redirects to our STS, STS performs multi-factor authentication, creates security token complying with WS-Federation and redirects back to OWA.
On OWA, the security token is verified successfully and the account on the Active Directory is verified.
Unfortunately, at the last step OWA enters a redirect loop which ends with an error code 0x80070057 in the Windows Event Log.
What could be causing this?
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