In the Azure portal on the overview page of your app you can click on "Endpoints". This will give you a list of relevant URLs including the "OpenID Connect metadata document" of the form https://login.microsoftonline.com/<your Directory (tenant) ID>/v2.0/.well-known/openid-configuration. From the docs we have
To use a provider other than Google, an OpenID Connect issuer must be defined on OAuth2.OpenIDConnectIssuer . The issuer must be an HTTPS URL and the location of the /.well-known/openid-configuration discovery metadata for OpenID Connect.
So OpenIDConnectIssuer should be set to https://login.microsoftonline.com/<your Directory (tenant) ID>/v2.0/.