This commit adds support for Kerberos authentication with a platinum
license. Kerberos authentication support relies on SPNEGO, which is
triggered by challenging clients with a 401 response with the
`WWW-Authenticate: Negotiate` header. A SPNEGO client will then provide
a Kerberos ticket in the `Authorization` header. The tickets are
validated using Java's built-in GSS support. The JVM uses a vm wide
configuration for Kerberos, so there can be only one Kerberos realm.
This is enforced by a bootstrap check that also enforces the existence
of the keytab file.
In many cases a fallback authentication mechanism is needed when SPNEGO
authentication is not available. In order to support this, the
DefaultAuthenticationFailureHandler now takes a list of failure response
headers. For example, one realm can provide a
`WWW-Authenticate: Negotiate` header as its default and another could
provide `WWW-Authenticate: Basic` to indicate to the client that basic
authentication can be used in place of SPNEGO.
In order to test Kerberos, unit tests are run against an in-memory KDC
that is backed by an in-memory ldap server. A QA project has also been
added to test against an actual KDC, which is provided by the krb5kdc
fixture.
Closes#30243
a525c36c60