mod_http_oauth2: Implement stateless dynamic client registration Replaces previous explicit registration that required either the additional module mod_adhoc_oauth2_client or manually editing the database. That method was enough to have something to test with, but would not probably not scale easily. Dynamic client registration allows creating clients on the fly, which may be even easier in theory. In order to not allow basically unauthenticated writes to the database, we implement a stateless model here. per_host_key := HMAC(config -> oauth2_registration_key, hostname) client_id := JWT { client metadata } signed with per_host_key client_secret := HMAC(per_host_key, client_id) This should ensure everything we need to know is part of the client_id, allowing redirects etc to be validated, and the client_secret can be validated with only the client_id and the per_host_key. A nonce injected into the client_id JWT should ensure nobody can submit the same client metadata and retrieve the same client_secret

TLS 1.0 and TLS 1.1 are about to be obsolete. This module warns clients
if they are using those versions, to prepare for disabling them.

# Configuration

``` {.lua}
modules_enabled = {
    -- other modules etc
    "warn_legacy_tls";
}

-- This is the default, you can leave it out if you don't wish to
-- customise or translate the message sent.
-- '%s' will be replaced with the TLS version in use.
legacy_tls_warning = [[
Your connection is encrypted using the %s protocol, which has been demonstrated to be insecure and will be disabled soon.  Please upgrade your client.
]]
```

## Options

`legacy_tls_warning`
:   A string. The text of the message sent to clients that use outdated
    TLS versions. Default as in the above example.

`legacy_tls_versions`
:   Set of TLS versions, defaults to
    `{ "SSLv3", "TLSv1", "TLSv1.1" }`{.lua}, i.e. TLS \< 1.2.