Fix: API Leakage (#328)

Co-authored-by: Daniel Heidemann <mail@dheidemann.de>

Author: Tim-Grube

server/graph/errors.go

@@ -0,0 +1,6 @@
+package graph
+
+import "fmt"
+
+var ErrInternal = fmt.Errorf("internal server error")
+var ErrWrongCredentials = fmt.Errorf("incorrect credentials provided")