export function decomposeJwt()

in src/jwt.ts [93:150]

• 50 lines of code
• 6 McCabe index (conditional complexity)

export function decomposeJwt(jwt: unknown): {
  header: JwtHeader;
  headerB64: string;
  payload: JwtPayload;
  payloadB64: string;
  signatureB64: string;
} {
  // Sanity checks on JWT
  if (!jwt) {
    throw new JwtParseError("Empty JWT");
  }
  if (typeof jwt !== "string") {
    throw new JwtParseError("JWT is not a string");
  }
  if (!jwt.match(/^[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+$/)) {
    throw new JwtParseError(
      "JWT string does not consist of exactly 3 parts (header, payload, signature)"
    );
  }
  const [headerB64, payloadB64, signatureB64] = jwt.split(".");

  // B64 decode header and payload
  const [headerString, payloadString] = [headerB64, payloadB64].map((b64) =>
    Buffer.from(b64, "base64").toString("utf8")
  );

  // Parse header
  let header: ReturnType<typeof safeJsonParse>;
  try {
    header = safeJsonParse(headerString);
  } catch (err) {
    throw new JwtParseError(
      "Invalid JWT. Header is not a valid JSON object",
      err
    );
  }
  assertJwtHeader(header);

  // parse payload
  let payload: ReturnType<typeof safeJsonParse>;
  try {
    payload = safeJsonParse(payloadString);
  } catch (err) {
    throw new JwtParseError(
      "Invalid JWT. Payload is not a valid JSON object",
      err
    );
  }
  assertJwtPayload(payload);

  return {
    header,
    headerB64,
    payload,
    payloadB64,
    signatureB64,
  };
}