axios-request-interceptor.js

const tokenChecker = (config) => {
  if (Transport.Http.isAccessTokenValid(config)) return config;
  try {
    Transport.Auth.fetchNewAccessTokenAsync().then((access) => {
      /*  Transport.Http.updateAuthorizationHeader accepts a token string
          then formats it into a proper Authorization header string.
          It then assigns that value to the axios instance's .defaults.headers.common.Authorization
          for future requests.
          Finally it returns that formatted header string for use by the caller.
          In this case, I want to add it to the current request before it goes out
          since its Authorization header is invalid.
      */
      config.headers.Authorization = Transport.Http.updateAuthorizationHeader(
        access,
      );
      return Promise.resolve(config);
    });
  } catch (e) {
    switch (true) {
      // handle various errors
    }
  }
  return config;
};


const successfulSignInSteps = (token) = {
  // ...
  Transport.Http.interceptors.request.use(tokenChecker);
  // ...
}