Securing Single Page Apps using the OAuth2 Implicit Grant Flow
Modern Single Page Applications are typically powered by a backend REST API, which needs to be secured against misuse. As the application lives entirely in the browser (user agent) of the end user, and does typically not have a server session, traditional approaches for this (server side sessions) are not desired.
In order to decouple the backend API and frontend application, an API Gateway can be put in place to implement the OAuth 2.0 Implicit Grant Flow or Authorization Code Grant with the PKCE extension, which is the recommended way of solving giving a "public" client (as opposed to a "confidential" client) access to an API.
For development time, the following workflow is typical:
response_type=code in the redirect parameters
For the OAuth2.0 Implicit Flow Grant and the Authorization Code Grant, it is strongly adviced against to also incorporate the client secret into the single page app; this would enable attackers to reverse engineer the app and extract the credentials. The client ID helps the authorization server to know exactly to which URL it will deliver the access token.
wicked supports both Flows, but the Authorization Code Grant is the flow which is recommended, being more secure.
To illustrate the runtime flow of such an authentication and authorization process using the OAuth 2.0 Implicit Flow Grant, see this picture:
Usually, the SPA will try to store an access token inside its local storage; in case there is none to use, or if it has expired, the SPA should redirect to the Authorization Server to get a new token or authorization code. Wicked supports "silent refreshes", which is the technique which is usually applied to refresh tokens in situations where refresh tokens do not exist.
When registering the application/client, you must specify that it's a Single Page Application (aka browser based application). This has certain effects on the Authorization Server, such as a refresh token is not being returned.
wicked.haufe.io has everything in the box to implement this type of workflow, using any identity provider you need, including wicked's own username/email and password store. Follow these steps:
Now application developers can sign up for using your API; the portal will help the developer to setup up the application and will also have help pages for the different flows (see Implicit Grant help page, and the Authorization Code Grant help page).