GetSubject extracts the subject (user ID) from a JWT token.

IsValidJWT is a custom validator to check if the provided string is a valid JWT token.

Parse function validates and extracts the JWT claims.

ClaimsKey is the context key for storing JWT claims in the request context.

TokenKey is the context key for storing the JWT token in the request context.

Add a custom Claims structure to include internal role, external roles, and permissions.