Permanent identifier

[maraino]

Description

This PR adds support for the Permanent Identifier SAN (#53). With this PR, a Permanent Identifier can be added to a template data using:

data.Set(x509util.SANsKey, []x509util.SubjectAlternativeName{
	{Type: x509util.PermanentIdentifierType, Value: permanentIdentifier},
})

It also cleans and adds more unit tests for custom SANs PR (#27), and updates go.step.sm/crypto CI to use Go 1.18 and Go 1.19

Note that the assigner part of the Permanent Identifier is currently not supported. Suggestions are welcome. One possible solution would be to convert the SubjectAlternativeName.Value to any and enforce string for most common types and support both string and a JSON for the Permanent Identifier. Other non-supported types like DirectoryNames can benefit from this. But if we want to do this, this will be part of a different PR.

[hslatman]

Your solution using any would result in a type switch to do something type specific when we support it, and do a transformation to a string when we don't know the type (yet)?

[maraino]

Your solution using any would result in a type switch to do something type specific when we support it, and do a transformation to a string when we don't know the type (yet)?

Yes, most of the types would be string, and fail if they are not, but we can add custom types for more complex SANs, although at this moment there's no real need for it, so if we need to it will go to a different PR.