how can I iterate over the available request headers?

[nikhedonia]

As far as I can see the only way to access headers is via request::headers(std::string key). It would be nice to have a list of available keys.

It would sufficient to expose the const-iterators of request::header_list. Shall I make a PR ?

[Jeffail]

Hey @nikhedonia. Sounds good, would be happy to take a pull request.