@AlokVenugopal
The "/nifi-api/access/token" endpoint is used by the ldap-provider or kerberos-provider NiFi login providers. Since you are using an OIDC (SSO) provider, you would need to obtain the token from that provider.
You can utilize the developer tools available in most browsers to capture the rest-api call being made to NiFi from you browser. While I do not have a setup utilizing Azure AD, I'd expect you should be able to see the redirect to the Azure endpoint to get the token.
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Thank you,
Matt