Forward soft argument to validate_signature

[neanias]

When calling the validate_document method chain, the soft parameter is passed down from one method to another except in the hand off from validate_document_with_cert to validate_signature.

[johnnyshields]

@neanias two questions:

1. Just checking Chesterton's Fence here, why do you think it might have been true in the first place?
2. What is your used case to have this pass in the soft arg?

[neanias]

For 1. I would think it was true in the first place because validation may have always wanted to be soft at this stage to avoid raising an error? It's a bit unusual to me in reading the git log that when the soft parameter was introduced for this method it was to allow surpressing exceptions, but there's no way to stop surpressing exceptions. I'm not clear if the tests are covering the unhappy path as a result since it doesn't check if passing soft = false raises an error.

For 2. it's been over a year since I opened this so I can't exactly remember why I opened the PR in the first place. I think I was trying to understand why my code wasn't throwing any errors when I passed in soft = false as per the docs.

[neanias]

The soft = true param was added in this commit: d0e117a

[johnnyshields]

OK. @pitbulk I think it's reasonable to merge this.

[pitbulk]

I remember I checked it time ago when was registered, but for some reason I did not merge it.

As "validate signature" is a critical piece, I will need more time to review this PR and check why it was implemented in that way.

[johnnyshields]

This change seems important for security.

The previous logic made signature validation always a soft validation. However, if one's system is relying on errors to be raised, then currently failed signature validation won't raise an error, and one will permit a failed signature validation when one should actually reject it! 😱

I can't imaginee a case where a user wants hard errors, but only wants signature validation to be soft.

Conversely, users using soft validations won't be affected at all.

[neanias]

Also realised that I didn't add tests to check that the right hard error is raised when soft is disabled. I'll add one now

[pitbulk]

If you check the use of validate_document_with_cert in the code, it is already used with soft parameter with true value, and the error is added as in the rest of validations.

[neanias]

I see. So does this method need to accept the soft flag at all then?