Hi people,

When reconnecting, `erc-determine-parameters' prefers reusing existing
session parameters, mainly by way of the various "compute" functions,
like `erc-compute-server'. But this isn't true if a parameter is nil.
The "danger" here is that, once exposed to new details, like the network
name, a custom auth-source-search function, for example, could reach a
different conclusion than it did initially, which could then lead to the
unwanted transmission of a non-server password via the PASS command.

One solution would be to just bypass `erc-determine-parameters' when
reconnecting and instead copy over all session vars verbatim while
leaving them unset in target buffers. However, there may be third-party
code expecting these vars to be recomputed whenever `erc-open' runs. So,
for the sake of compatibility, it's probably prudent to just focus on
`erc-session-password' for now because it's the likeliest offender (and
because passwords).

For this, we're mainly concerned with `erc-auth-source-server-function',
which always runs when reconnecting if the existing session password is
nil (and the opt itself is non-nil). One way to partially address this
might be to hide an existing "derived" `erc-network--id' from
`erc-auth-source-server-function' when reconnecting or opening a target
buffer. But this assumes a lot. Alternatively, we could just inhibit
`erc-auth-source-server-function' from running whenever
`erc--server-reconnecting' is non-nil and `erc-open' was called with a
nil session password, which is what this patch does.

(Better ideas welcome, as always.)

Thanks,
J.P.


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