Add custom policy claim name (#8764)

In certain organizations policy claim names
can be not just 'policy' but also things like
'roles', the value of this field might also
be *string* or *[]string* support this as well

In this PR we are still not supporting multiple
policies per STS account which will require a
more comprehensive change.

cmd/auth-handler.go

@@ -226,7 +226,7 @@ func getClaimsFromToken(r *http.Request) (map[string]interface{}, error) {
 		// If OPA is not set, session token should
 		// have a policy and its mandatory, reject
 		// requests without policy claim.
-		p, pok := claims[iamPolicyName()]
+		p, pok := claims[iamPolicyClaimName()]
 		if !pok {
 			return nil, errAuthentication
 		}