In the Securing Apps Guide there's "2.4.2.4. Client Credentials" chapter which is strongly related to Service Accounts but there's no mention of it.
Therefore, it would be a good idea to add a link to end of this chapter which would lead to "Service Accounts" [1] in Server Administration Guide.
Currently there's only link to OAuth 2.0 specification.

[1] https://access.redhat.com/documentation/en-us/red_hat_single_sign-on/7.1-beta/html-single/server_administration_guide/#service_accounts