Charset issue with Basic authentication

Hi,

I'm using PowerQuery as a datasource for an Excel worksheet. Data are exposed by a REST API supporting Basic Authentication. It is working well except when user name or password contains special characters like µ or é. It seems PowerQuery converts the provided "user:password" to US-ASCII during Basic authentication instead of using UTF-8. Spécial characters like µ and é are replaced with a "?" (char code 0x3F). Below is a Wireshark capture where I tried "µéè" as password and we can see it became "???":

I tried to add a "WWW-Authenticate" header on the 401 response with charset="UTF-8" in value like specified in the RFC : https://www.rfc-editor.org/rfc/rfc7617#section-2.1

WWW-Authenticate: Basic realm="simple", charset="UTF-8"

But it seems PowerQuery simply ignores this header because no more query is emitted after the first 401 Unauthorized.

I can workaround the problem using Anonymous authentication and providing the header manually:

let
    Auth = User & ":" & Password,
    Bytes = Text.ToBinary(Auth),
    Credentials = Binary.ToText(Bytes, BinaryEncoding.Base64),
    Source = Web.Contents("http://localhost:53671/7bc0cca0-f3ae-49ce-a229-d9daa0941103/TestBasicAuthentication/Get",    
    [
      Headers = [#"Authorization" = "Basic " & Credentials]
    ])
in
    Source

This solution works well but it is a security issue because the password would be exposed in clear text in the Excel file.

Is it possible to force Basic authentication to use UTF-8 encoding ?