init: add source code from src.zip

src/services/oauth/crypto.ts

@@ -0,0 +1,23 @@
+import { createHash, randomBytes } from 'crypto'
+
+function base64URLEncode(buffer: Buffer): string {
+  return buffer
+    .toString('base64')
+    .replace(/\+/g, '-')
+    .replace(/\//g, '_')
+    .replace(/=/g, '')
+}
+
+export function generateCodeVerifier(): string {
+  return base64URLEncode(randomBytes(32))
+}
+
+export function generateCodeChallenge(verifier: string): string {
+  const hash = createHash('sha256')
+  hash.update(verifier)
+  return base64URLEncode(hash.digest())
+}
+
+export function generateState(): string {
+  return base64URLEncode(randomBytes(32))
+}