Avoid Authorization headers when using Credential Type UsernamePassword

[Agazoth]

I use UsernamePassword to get information needed to build the uri string in a custom connector. The Password bit is unique for the file I want to retrieve when combined with the uri part in the Username bit.

[DataSource.Kind="MyConnector", Publish="MyConnector.Publish"]
shared MyConnector.Contents = () as table =>
    let
        baseUri = try Extension.CurrentCredential()[Username] otherwise "https://MyEndpoint",
        token = try Extension.CurrentCredential()[Password] otherwise "MySecretToken"
    in    
        GetMyData(baseUri, token);

MyConnector = [
    Authentication = [
         UsernamePassword = [
            UsernameLabel = "Url",
            PasswordLabel = "SecretToken"
         ],
        Implicit = []
    ],
    Label = "Uri token access"
];

GetMyData = (uri, token) =>
	let
	_uri = uri & '?' & token
	source = Json.Document(Web.Contents(_uri)),
	value = source[value],
	ConvertedToTable = Table.FromList(value, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
	fieldNames = Record.FieldNames(ConvertedToTable{0}[Column1]),
	final = Table.ExpandRecordColumn(ConvertedToTable, "Column1", fieldNames, fieldNames)

 in
	final;

Running the connector with Anonymous the call works. When selecting UsernamePassword authentication in my connector and filling in the exact same values as used in Anonymous, I get this error:

Authentication is not given in the correct format. Check the value of Authorization header

I assume this is caused by the built-in functionality, but I would like an option, where I can make my Web.Contents(_uri) call whithout an altered authentication header.

I have tried different ways to "heal" the header, to get my call through. Including;

Headers = []
and
Web.Contents(_uri), [ExcludedFromCacheKey = {"Authorization"}]

I might be going about this in the wrong way: What I really want to do is to give the enduser og my connector an option to fill in two variables that the connector then uses to build a Web.Contents() call that runs anonymous. How can this be achieved?