File

mod_tls: Enable Prosody's certificate checking for incoming s2s connections (fixes #1916) (thanks Damian, Zash) Various options in Prosody allow control over the behaviour of the certificate verification process For example, some deployments choose to allow falling back to traditional "dialback" authentication (XEP-0220), while others verify via DANE, hard-coded fingerprints, or other custom plugins. Implementing this flexibility requires us to override OpenSSL's default certificate verification, to allow Prosody to verify the certificate itself, apply custom policies and make decisions based on the outcome. To enable our custom logic, we have to suppress OpenSSL's default behaviour of aborting the connection with a TLS alert message. With LuaSec, this can be achieved by using the verifyext "lsec_continue" flag. We also need to use the lsec_ignore_purpose flag, because XMPP s2s uses server certificates as "client" certificates (for mutual TLS verification in outgoing s2s connections). Commit 99d2100d2918 moved these settings out of the defaults and into mod_s2s, because we only really need these changes for s2s, and they should be opt-in, rather than automatically applied to all TLS services we offer. That commit was incomplete, because it only added the flags for incoming direct TLS connections. StartTLS connections are handled by mod_tls, which was not applying the lsec_* flags. It previously worked because they were already in the defaults. This resulted in incoming s2s connections with "invalid" certificates being aborted early by OpenSSL, even if settings such as `s2s_secure_auth = false` or DANE were present in the config. Outgoing s2s connections inherit verify "none" from the defaults, which means OpenSSL will receive the cert but will not terminate the connection when it is deemed invalid. This means we don't need lsec_continue there, and we also don't need lsec_ignore_purpose (because the remote peer is a "server"). Wondering why we can't just use verify "none" for incoming s2s? It's because in that mode, OpenSSL won't request a certificate from the peer for incoming connections. Setting verify "peer" is how you ask OpenSSL to request a certificate from the client, but also what triggers its built-in verification.

# Teal definitions and sources

This directory contains files written in the
[Teal](https://github.com/teal-language/tl) language, a typed dialect of
Lua.  There are two kinds of files, `.tl` Teal source code and `.d.tl`
type definitions files for modules written in Lua. The later allows
writing type-aware Teal using regular Lua or C code.

## Setup

The Teal compiler can be installed from LuaRocks using:

```bash
luarocks install tl
```

## Checking types

```bash
tl check teal-src/prosody/util/example.tl
```

Some editors and IDEs also have support, see [text editor
support](https://github.com/teal-language/tl#text-editor-support)


## Compiling to Lua

`GNUmakefile` contains a rule for building Lua files from Teal sources.
It also applies [LuaFormat](https://github.com/Koihik/LuaFormatter) to
make the resulting code more readable, albeit this makes the line
numbers no longer match the original Teal source.  Sometimes minor
`luacheck` issues remain, such as types being represented as unused
tables, which can be removed.

```bash
sensible-editor teal-src/prosody/util/example.tl
# Write some code, remember to run tl check
make util/example.lua
sensible-editor util/example.lua
# Apply any minor tweaks that may be needed
```

## Files of note

`module.d.tl`
:	Describes the module environment.