OAuth 2.0 integration issue in JIRA AWS

[Revathi S]

We tried integrating OAuth with JIRA instance using Microsoft Service provider. But we are not able to establish the connection. Steps we followed-
1) Registered the jira application over microsoft service provider by our Azure Expert.
2) He generated client ID and Client secret and copied same to OAuth integration and gave him redirect URL link for configuration.
3) Once redirect url of JIRA is configured at microsoft level, tried "Test Connection"
4) It popped microsoft authorization page to login with email address as username and SSO password. After giving credentials , it keeps loading for 10-15min. Later throws 504 Gateway Time-out error else it throws "Proof Key for Code Exchange is required for cross-origin authorization code redemption." when tried on incognitive mode.

Could somebody help us what could be the reason for such error? We checked Atlassian logs nothing as such found. But through support zip and HAR file we found that the flow is making a request to https://login.microsoftonline.com/common/oauth2/v2.0/authorize but Jira does not received the reply from the endpoint, and eventually the request time-out resulting in the error. 

Please note we are not ready to expose our internal JIRA server to external/public server (Azure). So please let us know any alternative step to overcome this issue?

I think many of existing JIRA admins would have been gone through same issue when they integrate OAuth in JIRA and even won't be ready to expose their internal server to Azure. So in that case what is your best approach or solution?