Internet Explorer 11 replaces Authorization header

Question

What would cause Internet Explorer to replace the HTTP header

Authorization : Bearer <server-provided-token>

with

Authorization : Negotiate <some token>

when making an AJAX request?

Details

In Internet Explorer, some AJAX requests that are configured to contain the header Authorization: Bearer ... are being sent by Internet Explorer with the header Authorization: Negotiate ... instead.

For example, Fiddler shows that the first two of three requests contain the Authorization : Bearer... header, while the third suddenly contains the Authorization : Negotiate... header. The first two requests are successful, and the third fails because the request can't be properly authenticated.

All of the requests are constructed using the same client-side code, and are made one after another (within the span of a second). I have verified that the Authorization header correctly contains the Bearer token in all three cases up until the point the request is provided to the browser.

Also, I'm not seeing the same behavior in Chrome; it's only occurring in IE.

Request 1

GET http://localhost/myapp/api/User HTTP/1.1
Accept: application/json, text/plain, */*
Authorization: Bearer oEXS5IBu9huepzW6jfh-POMA18AUA8yWZsPfBPZuFf_JJxq-DKIt0JDyPXSiGpmV_cpT8FlL3D1DN-Tv5ZbT73MTuBOd5y75-bsx9fZvOeJgg04JcO0cUajdCH2h5QlMP8TNwgTpHg-TR9FxyPk3Kw6bQ6tQCOkOwIG_FmEJpP89yrOsoYJoCfrAoZ7M4PVcik9F9qtPgXmWwXB2eHDtkls44wITF_yM_rPm5C47OPCvMVTPz30KwoEPi6fHUcL3qHauP-v9uypv2e48TyPHUwLYmNFxyafMhBx4TkovnRcsdLHZiHmSjMq0V9a2Vw70
Referer: http://localhost/client/login.html
Accept-Language: en-US
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko
Host: localhost
DNT: 1
Connection: Keep-Alive

Request 2

POST http://localhost/myapp/api/Permissions HTTP/1.1
Referer: http://localhost/client/#/Dashboard
Content-Type: application/json
Authorization: Bearer oEXS5IBu9huepzW6jfh-POMA18AUA8yWZsPfBPZuFf_JJxq-DKIt0JDyPXSiGpmV_cpT8FlL3D1DN-Tv5ZbT73MTuBOd5y75-bsx9fZvOeJgg04JcO0cUajdCH2h5QlMP8TNwgTpHg-TR9FxyPk3Kw6bQ6tQCOkOwIG_FmEJpP89yrOsoYJoCfrAoZ7M4PVcik9F9qtPgXmWwXB2eHDtkls44wITF_yM_rPm5C47OPCvMVTPz30KwoEPi6fHUcL3qHauP-v9uypv2e48TyPHUwLYmNFxyafMhBx4TkovnRcsdLHZiHmSjMq0V9a2Vw70
Accept: application/json, text/plain, */*
Accept-Language: en-US
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko
Host: localhost
Content-Length: 1419
DNT: 1
Connection: Keep-Alive
Pragma: no-cache

<Post Data Removed>

Request 3

GET http://localhost/myapp/api/UserPreferences/Dashboard HTTP/1.1
Referer: http://localhost/client/#/Dashboard
Content-Type: application/json
Authorization: Negotiate YHsGBisGAQUFAqBxMG+gMDAuBgorBgEEAYI3AgIKBgkqhkiC9xIBAgIGCSqGSIb3EgECAgYKKwYBBAGCNwICHqI7BDlOVExNU1NQAAEAAACXsgjiBgAGADMAAAALAAsAKAAAAAYBsR0AAAAPVk1ERVZFTlYtU1JTQ0VSSVM=
Accept: application/json, text/plain, */*
Accept-Language: en-US
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko
Connection: Keep-Alive
DNT: 1
Host: localhost

The requests are being made via the AngularJS $http service, and the back-end is ASP.NET Web API hosted in IIS.

Answer 1

We had a problem where Internet Explorer was caching credentials. We could fix the problem by using the following script:

document.execCommand('ClearAuthenticationCache', 'false');

see: Wikipedia