mod_client_certs: do not crash on plain sockets In some situations (e.g., reverse-proxied websocket), non-TLS sockets can be marked as secure, causing mod_client_certs to call the undefined method getpeercertificate and crash.

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summary: Allow server administrators to probe any user
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This module lets server administrators send `<presence type="probe"/>`
to any local user and receive their presence in response, bypassing
roster checks.