TYK not able to resolve JWT token set in session metadata

Hi,

We are working on a use case where we are using Multiple Authentication Mechanism(Auth token and Custom plugin)
We have developed a Custom grpc plugin in Java. The plugin uses Ldap for aythentication and creates a signed JWT.The JWT is then stored The JWT is then stored inside the session object meta-data.

But when I am trying to pull the JWT inside the session metadata. The Gateway in the Global Header transform doesnot pulls the JWT from the session metadata and injects it into the header for use by the upstream.

“global_headers”: {
“Authorization”: “Bearer $tyk_meta.jwt”
},

I am following this repo for my Demo :https://github.com/TykTechnologies/tyk-grpc-go-basicauth-jwt.