Basic Auth Decoder

// Encode credentials to Basic Auth header
function encodeBasicAuth(username: string, password: string): string {
  const token = btoa(`${username}:${password}`);
  return `Basic ${token}`;
}

// Decode Basic Auth header
function decodeBasicAuth(header: string) {
  // Strip "Basic " prefix
  const b64 = header.replace(/^Basic\s+/i, "");
  const decoded = atob(b64);
  const [username, ...passwordParts] = decoded.split(":");
  return {
    username,
    password: passwordParts.join(":")
  };
}

console.log(encodeBasicAuth("admin", "pass123"));
// Basic YWRtaW46cGFzczEyMw==

// Use with fetch API
const headers = new Headers();
headers.set("Authorization",
  encodeBasicAuth("admin", "pass123"));
const res = await fetch("https://api.example.com", { headers });