feat: pubsub: add global signature policy

[wemeetagain]

See libp2p/specs#294 and libp2p/specs#299

Add a "global" signature policy to pubsub. This is a first-step towards having a "topic-specific" signature policy as described in the specs.
This "signature policy" replaces the ad-hoc options signMessages and strictSigning that were previously in use.

Only 'StrictSign' and 'StrictNoSign' signature policies are implemented, the 'LaxSign' and 'LaxNoSign' signature policies are not recommended and will be deprecated, so are not included.

BREAKING CHANGE:
signMessages and strictSigning pubsub configuration options replaced
with a globalSignaturePolicy option

[vasco-santos]

@wemeetagain is this ready for review? If so, can you get the linting fixed?

[wemeetagain]

@vasco-santos should be ready for a review

One thing that might be nice to add here, that isn't yet included:

• Using strict no-sign right now requires explicitly passing in a different msgId function. It may be nice to provide a default in that case, something with an implementation like hash(msg.data)

Do you have a preference for which library/hash could/should be used in this case?

[vasco-santos]

Overall this looks good. Just needs some minor changes and docs/examples update.

Can you update https://github.com/libp2p/js-libp2p-interfaces/tree/master/src/pubsub#example to use the policy? Might be worth documenting the constructor params in the API docs as well.
As the end goal is to support topic based policies, I think we should have tests for it, as well as an example in the README for the applications

[vasco-santos]

Using strict no-sign right now requires explicitly passing in a different msgId function. It may be nice to provide a default in that case, something with an implementation like hash(msg.data)

This is not included in go, right? We should leverage multiformats/js-multihashing-async

[wemeetagain]

This is not included in go, right? We should leverage multiformats/js-multihashing-async

Yea i don't think the go impl includes default msg id functions.

Is there a reason why we need the async version? Somehow it seems that a message id would be something that is always synchronously retrieved.

[vasco-santos]

Yea i don't think the go impl includes default msg id functions.

Ok, either way I think this is a nice addition!

Is there a reason why we need the async version? Somehow it seems that a message id would be something that is always synchronously retrieved.

Good point, we should use the base module then: https://github.com/multiformats/js-multihash

Furthermore, we should create an issue to track updating this to the topic level per the spec

[vasco-santos]

@wemeetagain Can you get the lint job fixed?

[vasco-santos]

LGTM

[wemeetagain]

bump

[jacobheun]

LGTM 🚢