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our outlook Add-in is working fine without implementation of MCAS(defender conditional access policy). when this policy is applied login process added few suffix like *.mcas.ms in the addin url. https://learn.microsoft.com/en-us/defender-cloud-apps/troubleshooting-proxy-url. i have added these suffix in the manifest with app url but failing to work. it works first time. user logout and re-login and now user get block when request raise for authentication. enter image description here also in manifest we have added. enter image description here

i tried adding these suffix in manifest but doesn't work

Sumit Jain
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  • What client are you using for this? Outlook Mac? Outlook Win32? Outlook Web Access? (as well as build versions) – Outlook Add-ins Team - MSFT Feb 27 '23 at 21:05
  • it is not working on any windows outlook client whether it is outlook 2016, 2019, M65 64 bit as well. build number for M365 MSO is - 16.0.16026.20196. – Sumit Jain Feb 28 '23 at 03:09
  • I got root cause. our Addin use dialog API for AAD auth flow in case of any error from AAD code flow for user interaction. Addin launch popup with domain url and redirect for AAD flow with prompt none. Client has custom MCAS proxy url like customurl.access.mcas.ms now this url is not define in Addin manifest therefore it auth flow not complete and getting proxy add_login error. Once i added clientcustomurl in AppDomain in Add-in manifest. it works fine. We need a way to add a generic url for this mcas issue since our application is multitenant and available on Office Store. Please help on it. – Sumit Jain Mar 01 '23 at 05:26

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