We're using Keycloak server for authenticating against several IDPS (google, active directory, etc). We have a spring gateway microservice which plays role of a client and several other microservices which play role of resource servers.

When user authenticates via keycloak, we want to associate the authenticated user with some custom fields (like context, roles, user details) from our custom database (NOT Keycloak DB) and send those fields to other microservices as well, so that we do not need to load the fields from DB in every microservice.

How would you do that? Making a GlobalFilter in the Gateway which would add those fields to request headers and setting those headers somehow to the principal object in resource servers? Or using cache (redis) to store the fields on gateway and load them in resource servers? Or do you have some other solution? For example extending access token, overiding UserDetailsService, etc..

What's important to note is, that we don't want to extends Keycloak Database, since we want to have the whole role management in our custom database. Reason for that is that keycloak schema is not very flexible. We want to use keycloak only as a dummy authentication server.

CodePudding user response：

The preferred option for security related values is for Keycloak to reach out to your APIs or custom data sources at the time of token issuance, then include your domain specific claims in JWT access tokens. In keycloak I believe this is done via a protocol mapper, as in this answer.

This design pattern is discussed in the Claims Best Practices article. It is recommended to not send secure values such as roles in custom headers etc, since they are potentially easier to change by a hostile party. Instead each API should receive the JWT and validate it, in a zero trust manner, then use the received claims for authorization.

For non secure values, such as a session_id or correlation_id used for logging, simple HTTP headers work well.