Currently there is a single route in slashing, so we can just forget about signing_info but I think we should re-think our routing a bit to allow this kind or requests easily.

Either having a keyword that says all but it's hacky and if we validate addresses or other parameters it won't work easily, we have to add conditions for that all around.

Usually I would like instead to push variables as close to the end as possible to avoid those cases, as when you do when you use the CLI.
/slashing/validators/{validatorPubKey}/signing_info -> /slashing/validators/signing_info/{validatorPubKey}

Or in distribution for example in:
/distribution/delegators/{delegatorAddr}/rewards -> /distribution/delegators/rewards/{delegatorAddr}
/distribution/delegators/{delegatorAddr}/rewards/{validatorAddr} -> /distribution/delegators/rewards/{delegatorAddr}/{validatorAddr}

Originally posted by @sabau in #3226 (comment)