FFR_LUA_ONLY_SIGNING cannot be enabled by using configure options

[futatuki]

The feature FFR_LUA_ONLY_SIGNING was added on 568adc1 in 2013-12-28. However its configure option was removed as "unknown feature", on 9628f53 in 2014-03-17, without changing the source code, including code for checking lua options in configure.ac.

Since then the feature cannot be enabled by using configure options.

It can be fix by one of below:

• add FFR_FEATURE([lua_only_signing], [Lua setup script exclusive signing control]) in configure.ac
• replace FFR_LUA_ONLY_SIGNING in source code to USE_LUA, and remove check for $enable_lua_only_signing in configure.ac, then enabled the feature when using lua, by default. As the feature does not take effect without adding LuaOnlySigning in opendkim.conf, it seems it is not harmful.
• remove this feature completely. It seems that this feature had not been used by anyone over 10 years.

[futatuki]

• remove this feature completely. It seems that this feature had not been used by anyone over 10 years.

I'm using lua script with KeyTable for issuing signing request, but I've never used this feature. It is sufficient not to specify SigningTable.

[thegushi]

FFR stands for "For Future Release", where it was written against an early version of a spec, or something that wanted more testing.

Given the release cadence we've had over the last few years, I'd say it's safe to remove most of these, especially given that they're not enabled by most OS packagers. I'm in favor of removing the code, @futatuki if you would like to give me a pull request, I'll happily merge it as soon as it passes the CI.

[futatuki]

Before making a pull request for removing the feature, I visited Feature Request #177 in SourceForge.

There was no feed back for proposed code from the author of the request. However I could imagine that this feature is useful if it were possible to lookup key entry from SigningTable via Lua function. Then they could achive their goal -- "... to call signfor with the SASL username instead of the sender and not sign if the session is not SASL-authenticated." by looking up SigningTable using SASL username, and then ignore SigningTable on embeded signing operation.

Anyways that is out of the scope of this issue. So if some one (or me?) interested in such a feature they should open another issue.

[futatuki]

... However I could imagine that this feature is useful if it were possible to lookup key entry from SigningTable via Lua function. Then they could achive their goal -- "... to call signfor with the SASL username instead of the sender and not sign if the session is not SASL-authenticated." by looking up SigningTable using SASL username, and then ignore SigningTable on embeded signing operation.

I didn't aware what odkim.signfor() does. This function looks up the SigningTable by any string passed as address and then make a request or multiple requests (or no request if no entry found) for the address. With that function, "LuaOnlySigning true" may be useful.