You could completely customize the login page with particular wordpress hooks so that it is effectively a login page.
Or you could try a plugin like this: https://wordpress.org/extend/plugins/custom-login/
This fits to the original question, so I am writing it here. What is the reason to have this bbp-login, bbp-register and bbp-lost-password code anyway? I’ve just spent a considerable amount of time customizing this bbp code to make it play nice with my theme. And then I had to realize that under certain circumstances the user ends up at the original WordPress login, register and lost password forms – which is certainly not waht I want. So why the … are those bbp forms there when obviously the original WordPress forms accomplish the same things. I could have customized the WordPress forms and all would have been good, no? To have this bbp forms seems to be redundant, confusing and – as it was in my case – time consuming. The bbp team, should supply such forms only if they go all the way, error detection and such included, or not supply it at all.
