Merge pull request #32906 from slaskawi/BZ1963198_multiple_idps_clarification

Bug 1963198: Add a note on configuring multiple IdPs

Author: bergerhoffer

modules/identity-provider-about-request-header.adoc

@@ -7,7 +7,9 @@
 
 A request header identity provider identifies users from request
 header values, such as `X-Remote-User`. It is typically used in combination with
-an authenticating proxy, which sets the request header value.
+an authenticating proxy, which sets the request header value. The
+request header identity provider cannot be combined with other identity providers
+that use direct password logins, such as HTPasswd, Keystone, LDAP or Basic authentication.
 
 [NOTE]
 ====