The REST API works endpoint allows users to return a list of selected fields, rather than the whole metadata record. You can do this by adding the select parameter to your query. This is useful if you are only interested in several of the metadata fields.
We have now added the resource field to the list of fields that can be selected, which means that you can return records containing only the resolution URL of a DOI. Here’s an example: https://api.crossref.org/v1/works?select=DOI,resource