Fix certificate file extensions

Closes: #75

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Use 8443 as the server port

Issue: #73

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Prompt for certificate before asking for password

Closes: #72

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>