api: Add go files

I know this is a huge commit, but I can't be bothered to check
this in part by part.

api/utils_crypto.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+)
+
+func randomHex(n int) (string, error) {
+	b := make([]byte, n)
+	if _, err := rand.Read(b); err != nil {
+		logger.Errorf("cannot create %d-byte long random hex: %v\n", n, err)
+		return "", errorInternal
+	}
+
+	return hex.EncodeToString(b), nil
+}