Add support for listing required delegations for an encrypted secret

This patch adds the /owners API endpoint that returns the list of users
that "own" the given secret. These are the users that can delegate their
passwords for decrypting the secret.

It also adds the "Get Owners" form in the web UI that uses the new API.

Fixes #62

core/core.go

@@ -73,6 +73,10 @@ type DecryptRequest struct {
 	Data []byte
 }
 
+type OwnersRequest struct {
+	Data []byte
+}
+
 type ModifyRequest struct {
 	Name     string
 	Password string
@@ -100,6 +104,11 @@ type DecryptWithDelegates struct {
 	Delegates []string
 }
 
+type OwnersData struct {
+	Status string
+	Owners []string
+}
+
 // Helper functions that create JSON responses sent by core
 
 func jsonStatusOk() ([]byte, error) {
@@ -366,3 +375,21 @@ func Modify(jsonIn []byte) ([]byte, error) {
 		return jsonStatusOk()
 	}
 }
+
+// Owners processes a owners request.
+func Owners(jsonIn []byte) ([]byte, error) {
+	var s OwnersRequest
+	err := json.Unmarshal(jsonIn, &s)
+	if err != nil {
+		log.Println("Error unmarshaling input:", err)
+		return jsonStatusError(err)
+	}
+
+	names, err := crypt.GetOwners(s.Data)
+	if err != nil {
+		log.Println("Error listing owners:", err)
+		return jsonStatusError(err)
+	}
+
+	return json.Marshal(OwnersData{Status: "ok", Owners: names})
+}