Refactoring error messages to use %w formatting directive and fix logging issue

[ChaosInTheCRD]

When looking at #293, it was clear that there were some issues occurring with formatting of error messages:

ERROR failed to create fulcio signer: %!w(*errors.errorString=&{square/go-jose: missing payload in JWS message})

After exploring this, it seemed that using fmt.Errorf to format the error first was the safer way to go, and using the %w formatting directive was worthwhile as it gives returned errors an Unwrap method for unwrapping the argument presented with %w initially (see here).

The result of the refactoring gives the following error message:
ERROR failed to create fulcio signer: square/go-jose: compact JWS format must have three parts

This PR coincides with PR in-toto/go-witness#83 created in the https://github.com/in-toto/go-witness repository.

Note: This is a proposed change to the structure. If anyone wishes to suggest a better way of structuring this I am all ears!

[jkjell]

Same question as the other PR, any reason to not have this as a single line with log.Errorf()

[ChaosInTheCRD]

Hey 👋 - I answered in the other PR: in-toto/go-witness#83 (comment)

[kriscoleman]

I went and checked out the other PR but didn't see an explanation for this line break?

[ChaosInTheCRD]

sorry if this was all very unclear. The reason for the splitting out the error formatting to fmt.Errorf is because log.Errorf does not support the %w directive. The reason for not having it all on a single line (e.g., log.Errorf(fmt.Errorf(... was for ease of readability.

After being round the houses with all of this a little bit, I believe we can switch all this to a log.WithError(err).Error(.... I will push said changes to this PR 😄

[kriscoleman]

Thanks for the contribution!!

[ChaosInTheCRD]

logs are not printing correctly after these changes, but this is just because the fix is made in in-toto/go-witness#85 and therefore won't be utilised in in-toto/witness until a new release of in-toto/go-witness is cut.

This has been tested against go-witness with the logging interface changes made and things are working as expected.

ERROR failed to create fulcio signer: square/go-jose: compact JWS format must have three parts

[jkjell]

Looks good!