Situation is like this:
- You got an AccessToken and RefreshToken (AT and RT for now on)
- Every API call needs to contain the AT
- When the AT expires you need to refresh it using your RT
Interceptor: Attaching Access Token to every network request
What you need is a Network Interceptor. Interceptors are a very powerful mechanism to rewrite calls. After hooking the interceptor to the OkClient every single call will pass through it. That is the perfect moment to attach your AT:
@Override
public Response intercept(Chain chain) throws IOException {
Request originalRequest = chain.request();
// Add authorization header with updated authorization value to intercepted request
Request authorisedRequest = originalRequest.newBuilder()
.header(AUTHORIZATION, accessToken)
.build();
return chain.proceed(authorisedRequest);
}
You can tweak this interceptor to handle edge cases. For example, when your accessToken is empty or when the request already contains an authorization header you may want to skip the rebuild. This can easily be done:
@Override
public Response intercept(Chain chain) throws IOException {
Request originalRequest = chain.request();
// Nothing to add to intercepted request if:
// a) Authorization value is empty because user is not logged in yet
// b) There is already a header with updated Authorization value
if (authorizationTokenIsEmpty() || alreadyHasAuthorizationHeader(originalRequest)) {
return chain.proceed(originalRequest);
}
// Add authorization header with updated authorization value to intercepted request
Request authorisedRequest = originalRequest.newBuilder()
.header(AUTHORIZATION, authorizationValue)
.build();
return chain.proceed(authorisedRequest);
}
Authenticator: Refreshing Access Token
How do you know it is time to refresh your AT? This is the approach:
- Monitor to network calls looking for errors.
- Whenever you get a
401 Not Authorisedit means your AT is no longer valid. - Refresh AT using RT.
- Repeat failed call.
This can be accomplish with Interceptors as well, but there is a much better way: Authenticators an interface designed specifically for this purpose.
When you set up an Authenticator OkHttp client will automatically ask the Authenticator for credentials when a response is 401 Not Authorised retrying last failed request with provied new credentials.
@Override
public Request authenticate(Proxy proxy, Response response) throws IOException {
// Refresh your access_token using a synchronous api request
newAccessToken = service.refreshToken();
// Add new header to rejected request and retry it
return response.request().newBuilder()
.addHeader(AUTHORIZATION, newAccessToken)
.build();
}
Setting everything up
Create an OkHttpClient and attach your NetworkInterceptor and yourAuthenticator to it
OkHttpClient okHttpClient = new OkHttpClient();
okHttpClient.networkInterceptors().add(authInterceptor);
okHttpClient.setAuthenticator(authAuthenticator);
Then use this client when creating your Retrofit RestAdapter
RestAdapter restAdapter = new RestAdapter.Builder()
.setEndpoint(ENDPOINT)
.setClient(new OkClient(okHttpClient))
.build();
return restAdapter.create(API.class);
Make Things Happen 