Use keycloak token for authentication

policy/diamond/policy/token/token.rego

@@ -2,10 +2,29 @@ package diamond.policy.token
 
 import rego.v1
 
-verify(token) := profile.sub if {
-	profile := http.send({
-		"url": opa.runtime().env.USERINFO_ENDPOINT,
-		"method": "GET",
-		"headers": {"authorization": token},
-	})
-}
+fetch_jwks(url) := http.send({
+	"url": url,
+	"method": "GET",
+	"force_cache": true,
+	"force_cache_duration_seconds": 86400,
+})
+
+jwks_endpoint := opa.runtime().env.JWKS_ENDPOINT
+
+issuer := opa.runtime().env.ISSUER
+
+unverified := io.jwt.decode(input.token)
+
+jwt_header := unverified[0]
+
+jwks_url := concat("?", [jwks_endpoint, urlquery.encode_object({"kid": jwt_header.kid})])
+
+jwks := fetch_jwks(jwks_url).raw_body
+
+verified := io.jwt.decode_verify(input.token, {
+	"cert": jwks,
+	"iss": issuer,
+	"aud": input.audience,
+})
+
+claims := verified[2] if verified[0]