GetOnPremisesRequestDigestAsync does not enforce windows authentication when multiple authentications are enabled on SharePoint Subscription Edition. Related to issue #889

[pbharani]

We have the same issue in SharePoint subscription edition that has both OIDC and ntlm enabled, while trying to fetch the apps from appcatalog for installation on a sitecollection using csom. var appFromCatalog = appManager.GetAvailable() throws 403.
Usual context building works when we use e.WebRequestExecutor.RequestHeaders.Add("X-FORMS_BASED_AUTH_ACCEPTED", "f"); and context.AuthenticationMode = ClientAuthenticationMode.Default; However while trying to get apps from appcatalog using appmanager.GetAvailable(), though the context has both context.AuthenticationMode = ClientAuthenticationMode.Default; and e.WebRequestExecutor.RequestHeaders.Add("X-FORMS_BASED_AUTH_ACCEPTED", "f"); set, still we get 403 thrown.