implemented grups api endpoint

api/v1/api_groups.go

@@ -30,6 +30,10 @@ import (
 
 func (api *API) ListGroups() http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		sendWebResponse(w, http.StatusNotImplemented, ErrorResponse{"listing groups not yet implemented"})
+		groups, err := api.store.ListGroups()
+		if err != nil {
+			sendWebResponse(w, http.StatusInternalServerError, ErrorResponse{err.Error()})
+		}
+		sendWebResponse(w, http.StatusOK, GroupsListing{groups})
 	})
 }

api/v1/types.go

@@ -38,7 +38,9 @@ type APIListing struct {
 }
 
 // Groups
-// TODO: add me
+type GroupsListing struct {
+	Groups []string `json:"groups"`
+}
 
 // Imports
 // TODO: add me