Allows users to authenticate without password via XMPP and for visitors to be filtered by XMPP verification.
On the web side, the XEP-0070 uses RFC-2617, which is a common way to authenticate to websites. On the XMPP-side, RFC-6120 and XEP-0070 have a nice way for clients which do not understand a given feature for falling back into a message to answer, as though it was a discussion.
So hopefully it "should" work in most case with not-too broken web browser or IM client. For IM clients, it should work (tested or reported by someone) with Psi, Gajim, OneTeam… In particular, it is known not to work with Pidgin, Adium, Swift, and the GoogleMail web interface.
You should check the Installation/dependencies section. Some PHP modules are necessary. If you are administrator or have flexible administrators, this will be very easily fixable (follow my instructions in the "dependencies" section). If you use a public service, which did not install these dependencies by default, and where you cannot have anything installed, then I am sorry but my plugin unfortunately won't work for you (actually for PEAR modules, you may add them by hand, as they are pure PHP. But you would need to be developers for the manipulation).
This means that your server uses TLS (and that's good!) but simply I did not package the certificate of their CA into my plugin. Please just tell me (see "Contacts" section) your server, I will check the CA and if it is an acceptable one, I will add its certificate.
It may also mean that the server certificate is self-signed, which is really not secure. If many servers are this way, I may consider adding an option to force such connection, but I would prefer not. If this happens to you, I would rather suggest you to change the server of your bot for one where security matters.