Using the OAuth 2 Implicit Flow¶
An app that needs access to an OAuth-protected back-end API on behalf of a user must obtain an Access Token. If the app can not keep a secret (i.e., it is deployed in an environment where users have access to its protected storage or communications), there is no added security in authenticating the app to the token endpoint as in the code flow. The Implicit Flow was specified exactly for this case, where the user is authenticated by the Authorization Server, and an Access Token is returned to the app directly in the fragment of a redirect URL.
This tutorial builds on the configuration setup in the "Setup and Getting Started" section and the "Setup a Username Authenticator". If you haven't done those steps yet you can visit those guides here:
It's possible to run this tutorial on a custom setup also, but the URLs may be different, as well as the capabilities configured in the profiles.
- Browser redirects to the Authorize endpoint of the OAuth Server
- If the user isn't authenticated the OAuth Server redirect to the Authentication Service
- The User authenticates, and is redirected back to the OAuth Server
- The OAuth Server issues the Access Token immediately and redirects back to the client
Because the app is not capable of keeping a secret, there is no long-lived, Refresh Token issued in this flow. Also, the issued Access Token should have a limited lifetime. Because an Access Token is returned in the fragment of the URI, it should not be cached or stored by intermediate systems or proxies. The security of the process relies on this property, as an Access Token should not be exposed to any party except the app.
For reference, the Implicit Flow is documented in section 4.2 of the OAuth 2.0 Specification.
To learn more about the client parameters of the Implicit flow see OAuth Implicit Flow.
Setup in Curity¶
Visit the Profiles screen and click the Token Service. On the right select Clients and click New.
Give the client an ID (eg.
spa for a single page website client).
Scroll down to the Capabilities section and click Add capabilities.
Select the Implicit Flow capability and click Next.
The redirect URL is back at the client. If you don't know what you will use just enter
http://localhost/callback for now. This can be changed later. This tutorial will manually run the flow so localhost is fine.
For user authentication select the authenticator created in the authenticator tutorial.
Add the openid Scope¶
We will also run the OpenID Code flow, so add the
openid scope to the client by scrolling down to the Permissions section of the client.
Make sure to remember to commit the changes in the Changes -> Commit menu.
Making Requests with the Client¶
With the default configuration we've setup, the server's authorization endpoint is at
https://localhost:8443/oauth/v2/oauth-authorize. If you are not using that configuration, determine the URL of your authorization endpoint, and adjust the following requests accordingly. To use the implicit flow, an app would create a URL to this endpoint, and redirect the user to it. The URL looks like this:
You can pretend to be the app, and enter this URL in a browser yourself. As a result, you will be asked to authenticate, after which Curity will redirect you back to the app by adding the token response parameters to the configured redirect URI, e.g.:
In case you want to request an ID Token as well, it turns into an OpenID Connect request, and for that you will need to include the
nonce parameters in the request:
After doing so, you should receive an ID token on the fragment of the callback URI.
If the app needs an ID token and an access token, the
response_type request parameter should include both
token, like this: