Azure AD for authentication and Third Party app (my legacy one) for authorization

Question

Hi

I have a legacy backend application used to provide authentication and authorization for an website. But now I need to grant access for Azure AD users to that website in a SSO fashion.

Nonetheless I have a lot of pages in that website and tons of microservices under authorization scopes defined by my legacy backend app.

I couldn't find in Azure AD solutions a way to authenticate using Azure AD features (OIDC, SAML, Oauth2) but browse my website using my legacy jwt token from my legacy authentication backend which has all authorization scopes spread through my whole system.

Appreciate any help

Thanks