Dropbox

Dropbox returns a 400 error if no Authorization header is present, rather than a 401. This means the interceptor cannot intercept such a response and attempt an authorization. The best workaround is to add a fake Authorization header if the data loader is to be used or simply do manual authorization.

Example code, courtesy of @salexkidd: https://github.com/p2/OAuth2/pull/270#issuecomment-398996766

func postRequest(path: String, callback: @escaping ((OAuth2JSON?, Error?) -> Void)) {
    let url = baseURL.appendingPathComponent(path)
    var req = oauth2.request(forURL: url)
    req.httpMethod = "POST"
    req.addValue("application/json", forHTTPHeaderField: "Content-type")
    
    if req.value(forHTTPHeaderField: "Authorization") == nil {
        req.setValue("Bearer 0000", forHTTPHeaderField: "Authorization")
    }
    ...
}