As dorko mentions you can check if Net::SSLeay is installed. However to enable HTTPS support for LWP this is only a part of what is needed. HTTPS support for LWP depends on LWP::Protocol::https which on its turn depends on IO::Socket::SSL, and that depends on Net::SSLeay.

So the correct way to enable HTTPS support for LWP is:

I do not know about the other backends.