How do I display annotations for signatures?

[yoyomo]

I found in mozilla's pdfjs that rendering an annotation is depending on the isRenderable property, and for Signatures, that property depends on hasOwnCanvas. But I do not find anywhere where that can be set. So as a workaround I mutated the annotation after onGetAnnotationsSuccess is called, checked if the fieldType was "Sig" and set hasOwnCanvas to true. Although it does work, it feels hacky and was wondering if there was a more proper way. Can't find anything in the documentation, only issues that do not say how