docs: def verify_claims(app_req, issuer=None):
      """
      Verify JWT claims.
  
      All times must be UTC unix timestamps.
  
      These claims will be verified:
  
      - iat: issued at time. If JWT was issued more than an hour ago it is
        rejected.
      - exp: expiration time.
  
      All exceptions are derived from
      :class:`mozpay.exc.InvalidJWT`.
      For expirations a
      :class:`mozpay.exc.RequestExpired`
      exception will be raised.
      """
      if not issuer:
          issuer = _get_issuer(app_req=app_req)
      try:
          float(str(app_req.get('exp')))
          float(str(app_req.get('iat')))
      except ValueError:
          _re_raise_as(InvalidJWT,
                       'JWT had an invalid exp (%r) or iat (%r) '
                       % (app_req.get('exp'), app_req.get('iat')),
                       issuer=issuer)