Office 365 using the Microsoft Graph API doesn't support GCC customers

Issue Summary

Since Jira Service Management 5.8.0, support to connect mail channels to Office 365 accounts using OAuth 2.0 as the authentication method and MS Graph API as the protocol has been introduced, as per https://jira.atlassian.com/browse/JSDSERVER-12419.

However, this new integration doesn't support GCC (Government Community Cloud) accounts.

It isn't supported because regular Office 365 accounts connect to graph.microsoft.com to fetch emails via the MS Graph API protocol, whilst GCC accounts connect to graph.microsoft.us.

Therefore, the connection is not established and the mail channel can't be connected using the domain graph.microsoft.com which is hardcoded and which cannot be configured via the UI.

Screenshots

As shown in the screenshots below showing the JSM Mail Channel configuration:

• when choosing Microsoft as the provider, there is no option to change the domain from graph.microsoft.com to graph.microsoft.us
  
• when choosing Custom as the provider, it is possible to change the mail server domain, but it is not possible to select MS Graph API as the protocol:
  

Therefore none of these providers can be configured to use GCC accounts.

Workaround

To be added later.