Integrate SAML with a GraphQL Node.js server already using JWT

I have a Node.js GraphQL server built using apollo-server running in production for the past one year. Authorization is handled by means of the graphql-shield library and JWT tokens in the request Authorization header.

Now, we have a new enterprise client and they want to log in via SAML using their server as IdP and obviously, ours will be the SP.

How can I send back a JWT token to the client once the SAML authentication is successfully completed? What is the right way to do handle this sort of a situation so I don’t have to re-architecture how we handle authorization throughout our server and continue using JWT?