The master branch of libssh2 supports wolfSSL natively, but this hasn't made it into a release, yet. If you're using libssh2 1.10.0 or older, you will need to use the approach described below.

• Configure wolfSSL with ./configure --enable-libssh2. Add --enable-debug if you're going to be debugging. Add --enable-fips=v2 if using wolfSSL FIPS.
• make and sudo make install wolfSSL into /usr/local.
• Download libssh2-1.9.0 with curl -O https://www.libssh2.org/download/libssh2-1.9.0.tar.gz.
• Unarchive this tar ball with tar xvf libssh2-1.9.0.tar.gz and cd libssh2-1.9.0.
• Apply the libssh2-1.9.0.patch file with patch -p1 < libssh2-1.9.0.patch (assuming the patch file is in the libssh2-1.9.0 directory; adjust the path according to your situation).
• Regenerate the configure script with ./buildconf.
• Configure libssh2 with ./configure --with-crypto=wolfssl --with-wolfssl=/usr/local. Update the path if you've installed wolfSSL using a different prefix than /usr/local.
• Run make to compile.
• Ensure all tests pass with make check.