Tested with development version 9184a75a21;
$ git clone https://github.com/obgm/libcoap --recursive
$ cd libcoap
$ ./autogen.sh
$ ./configure --enable-dtls --with-tinydtls --disable-shared
$ cd examples
$ ./coap-server -A ::1 -k 1234 &
$ ./coap-client 'coaps://[::1]/' -k 1234 -u CoAP
This is a test server made with libcoap (see https://libcoap.net)
Copyright (C) 2010--2016 Olaf Bergmann <bergmann@tzi.org>
PS. I added the --disable-doxygen line at configuration as well because those tools aren't installed here.