Why is the scheme required for AuthenticationHeaderValue?

Question

I am setting the authorization header of an HttpClient in the following manner:

httpClient
    .DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(null, "abc");

...but am getting the exception:

"scheme" of the AuthenticationHeaderValue cannot be null.

Why must the AuthenticationHeaderValue have a scheme? Is this required by a specific RFC?

Answer 1

The scheme is used to determine what kind of authentication you are using:

• Basic
• Oauth
• Bearer
• Digest
• etc.

The header will look like this:

{
   "key": "Authorization",
   "value": "<scheme> <parameter>"
}

Try to use Postman to see what is generated based on the different types of authentication supported by HTTP.