Implement Web Push API Go library with VAPID support and pluggable storage

Co-authored-by: imjasonh <210737+imjasonh@users.noreply.github.com>

vapid/vapid.go

@@ -0,0 +1,18 @@
+// Package vapid provides VAPID (Voluntary Application Server Identification)
+// utilities for Web Push.
+package vapid
+
+import (
+	"encoding/base64"
+)
+
+// ApplicationServerKey returns the VAPID public key formatted for use with
+// the JavaScript PushManager.subscribe() method.
+func ApplicationServerKey(publicKey []byte) string {
+	return base64.RawURLEncoding.EncodeToString(publicKey)
+}
+
+// DecodeApplicationServerKey decodes a base64 URL-encoded application server key.
+func DecodeApplicationServerKey(key string) ([]byte, error) {
+	return base64.RawURLEncoding.DecodeString(key)
+}