Implement OpenID token expressions evaluation

[ErmakovDmitriy]

This PR implements an OpenID token expression evaluation.

The idea and the use-case is to be able to define different behavior in HAProxy based on OpenID token claims.

An example:

• An OpenID token contains a field roles which is an array of admin, viewer, editor;
• We want to allow access to /admin URL path only for people with admin role;

With this PR, it is possible to define in HAProxy:

acl host1.example.com hdr(host) -i host1.example.com
acl host1.example.com_admin_path path_beg -i /admin
acl host1.example.com-admin-allowed var(sess.auth.token_expression_in_roles_admin) -m bool

http-request send-spoe-group spoe-auth try-auth-all if host1.example.com
http-request set-var(req.oidc_token_expressions) str("in;roles;admin") if host1.example.com
http-request send-spoe-group spoe-auth try-auth-all if host1.example.com

use_backend haproxy-spoe-auth-error if host1.example.com oauth2_error
use_backend haproxy-spoe-auth-redirect if host1.example.com !oauth2_authenticated

http-request deny deny_status 403 if host1.example.com !host1.example.com-admin-allowed host1.example.com_admin_path oauth2_authenticated
use_backend host1.example.com-backend if host1.example.com host1.example.com-admin-allowed