[boost] How do I authenticate myself?

I want to clone the current develop branch to verify that a bugfix to a trac item I opened does actually fix the bug. It seems like this information should be easy to find on the boost webpage or wiki, but neither of both explain how to authenticate myself when using “git clone --recursive git@ github.com:boostorg/boost.git modular-boost >clone.log”. The output of this is “Permission denied (publickey)”, which seems to mean to me that I need a ssh key the server actually knows about or that I have to upload my public key somehow. Have I just missed something on the wiki? --- Felix Uhl