How I am currently doing this is, sending a raw JSON through Postman. This JSON is used to create a Case record in Salesforce. In order to attach a file to that case, the JSON contains a base64 encoded file content, which could be used for attachment.
When I send a multipart/form-data, postman throws
You have sent us an Illegal URL or an improperly formatted request.
I also remember reading somewhere that
Apex REST does not support multipart/form-data requests.
Is there any workaround for this?