What this means is that both representations are valid:
aiohttp = { git = "git@github.com:aio-libs/aiohttp.git" }
aiohttp = { git = "ssh://git@github.com/aio-libs/aiohttp.git" }
but they must both translate to the following PEP-508 representation:
aiohttp @ git+ssh://git@github.com/aio-libs/aiohttp.git