add logging for signature string build error

[hansihe]

No description provided.

[voltone]

Thanks for your PR! It seems risky to inspect the exception, as the block in which the exception occurs has access to conn, which might contain information that should not be logged.

In general I try to avoid logging messages from code that can't be customized, as not everyone will have the same expectations of what should or should not be logged. So ideally any logging behaviour should live in the success or failure callbacks, so they can be customized by the user of the plug.

Is there any particular issue you ran into that resulted in a "could not build signature_string" error? Maybe we can improve the error handling within that function to (selectively) return a more detailed error, which can then be logged in the failure callback?

[hansihe]

Sorry about this, I meant to open the PR on the fork itself, but I accidentally opened it on the upstream :)

I fully agree this should not be merged, this was meant to be used by us internally and temporarily to debug some issues in our system.