The following PRs:

1. Initial commit of safe url resolver #1910
2. SWG-7516 utilizing safeURLResolver in swagger-parser-v3 #1911

Added a possibility for swagger-parser to provide a Allow & Block list when resolving external refs. Thanks to that, it is possible provide additional security layer when using this tool inside services. This functionality is still missing when resolving 3.0 and 2.0 versions of OAS.

I've the proposal of the code prepared, so I'll put it on the PR when done.