Simple attributes can be added easily (it's as simple as adding form fields with an id of `user.attribute.company`), but anything requiring access restrictions (only an admin can update, for example) will require custom development.

The Profile SPI in the works hopes to make this much easier, you can track the progress on that on the JBoss JIRA tracker [0].

[0]: https://issues.redhat.com/browse/KEYCLOAK-2966