Security Context does not convert text value to JSON

**Describe the bug**
I am trying to use security context with Cognito and JWT. As per your documentation we generate JWT. The response is like:

` "user": "{\"company_id\":\"moleculedata\",\"user_id\":\"5badab3e-1e5d-4414-8a80-269fdaf2ff8e\",\"roles\":[\"user\"]}"`

similar to example in the documentation [https://cube.dev/docs/security/jwt/aws-cognito]

when I try to use it with CUBEJS_JWT_CLAIMS_NAMESPACE=user, I get an error in the playground:

`TypeCannot create proxy with a non-object as target or handler`

I hope to use the values inside user key form JWT.

If any questions, please let me know.

Kind regards,
Rytis