Add tokeninfo endpoint

api/token.go

+package api
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"github.com/bolkedebruin/rdpgw/security"
+	"log"
+	"net/http"
+)
+
+func (c *Config) TokenInfo(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodGet {
+		http.Error(w, "Invalid request", http.StatusMethodNotAllowed)
+		return
+	}
+
+	tokens, ok := r.URL.Query()["access_token"]
+	if !ok || len(tokens[0]) < 1 {
+		log.Printf("Missing access_token in request")
+		http.Error(w, "access_token missing in request", http.StatusBadRequest)
+		return
+	}
+
+	token := tokens[0]
+
+	info, err := security.UserInfo(context.Background(), token)
+	if err != nil {
+		log.Printf("Token validation failed due to %s", err)
+		http.Error(w, fmt.Sprintf("token validation failed due to %s", err), http.StatusForbidden)
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json; charset=UTF-8")
+	if err = json.NewEncoder(w).Encode(info); err != nil {
+		log.Printf("Cannot encode json due to %s", err)
+		http.Error(w, "cannot encode json", http.StatusInternalServerError)
+		return
+	}
+}
\ No newline at end of file

main.go

@@ -130,6 +130,7 @@ func main() {
 	http.Handle("/remoteDesktopGateway/", common.EnrichContext(http.HandlerFunc(gw.HandleGatewayProtocol)))
 	http.Handle("/connect", common.EnrichContext(api.Authenticated(http.HandlerFunc(api.HandleDownload))))
 	http.Handle("/metrics", promhttp.Handler())
+	http.HandleFunc("/tokeninfo", api.TokenInfo)
 	http.HandleFunc("/callback", api.HandleCallback)
 
 	err = server.ListenAndServeTLS("", "")

security/jwt.go

@@ -145,6 +145,69 @@ func GenerateUserToken(ctx context.Context, userName string) (string, error) {
 	return token, err
 }
 
+func UserInfo(ctx context.Context, token string) (jwt.Claims, error) {
+	standard := jwt.Claims{}
+	if len(UserEncryptionKey) > 0 && len(UserSigningKey) > 0 {
+		enc, err := jwt.ParseSignedAndEncrypted(token)
+		if err != nil {
+			log.Printf("Cannot get token %s", err)
+			return standard, errors.New("cannot get token")
+		}
+		token, err := enc.Decrypt(UserEncryptionKey)
+		if err != nil {
+			log.Printf("Cannot decrypt token %s", err)
+			return standard, errors.New("cannot decrypt token")
+		}
+		if _, err := verifyAlg(token.Headers, string(jose.HS256)); err != nil {
+			log.Printf("signature validation failure: %s", err)
+			return standard, errors.New("signature validation failure")
+		}
+		if err = token.Claims(UserSigningKey, &standard); err != nil {
+			log.Printf("cannot verify signature %s", err)
+			return standard, errors.New("cannot verify signature")
+		}
+	} else if len(UserSigningKey) == 0 {
+		token, err := jwt.ParseEncrypted(token)
+		if err != nil {
+			log.Printf("Cannot get token %s", err)
+			return standard, errors.New("cannot get token")
+		}
+		err = token.Claims(UserEncryptionKey, &standard)
+		if err != nil {
+			log.Printf("Cannot decrypt token %s", err)
+			return standard, errors.New("cannot decrypt token")
+		}
+	} else {
+		token, err := jwt.ParseSigned(token)
+		if err != nil {
+			log.Printf("Cannot get token %s", err)
+			return standard, errors.New("cannot get token")
+		}
+		if _, err := verifyAlg(token.Headers, string(jose.HS256)); err != nil {
+			log.Printf("signature validation failure: %s", err)
+			return standard, errors.New("signature validation failure")
+		}
+		err = token.Claims(UserSigningKey, &standard)
+		if err = token.Claims(UserSigningKey, &standard); err != nil {
+			log.Printf("cannot verify signature %s", err)
+			return standard, errors.New("cannot verify signature")
+		}
+	}
+
+	// go-jose doesnt verify the expiry
+	err := standard.Validate(jwt.Expected{
+		Issuer: "rdpgw",
+		Time: time.Now(),
+	})
+
+	if err != nil {
+		log.Printf("token validation failed due to %s", err)
+		return standard, fmt.Errorf("token validation failed due to %s", err)
+	}
+
+	return standard, nil
+}
+
 func getSessionInfo(ctx context.Context) *protocol.SessionInfo {
 	s, ok := ctx.Value("SessionInfo").(*protocol.SessionInfo)
 	if !ok {
@@ -153,3 +216,12 @@ func getSessionInfo(ctx context.Context) *protocol.SessionInfo {
 	}
 	return s
 }
+
+func verifyAlg(headers []jose.Header, alg string) (bool, error) {
+	for _, header := range headers {
+		if header.Algorithm != alg {
+			return false, fmt.Errorf("invalid signing method %s", header.Algorithm)
+		}
+	}
+	return true, nil
+}
\ No newline at end of file