We're trying to move an ASP.NET MVC application, which uses DotNetOpenAuth OpenID Version 3.4.1, from a single server web garden to a physical server cluster held behind a hardware load balancer.

Our old setup (OpenID RP working):

Browser => SHTTP => Server => WebGarden => Nonce/Session Store

Our new setup (OpenID RP not working):

Browser => SHTTP => Load Balancer => HTTP => Cluster Node => WebGarden => Nonce/Session Store DB

When we authenticate with the new setup we are correctly redirected to the OpenID Provider but after authenticated we are redirected back to our cluster (relay party) and get the following exception:

Exception

DotNetOpenAuth.Messaging.ProtocolException: Redirects on POST requests that are to untrusted servers is not supported.
 at DotNetOpenAuth.Messaging.ErrorUtilities.VerifyProtocol(Boolean condition, String message, Object[] args) in c:\TeamCity\buildAgent\work\bf9e2ca68b75a334\src\DotNetOpenAuth\Messaging\ErrorUtilities.cs:line 235
 at DotNetOpenAuth.Messaging.UntrustedWebRequestHandler.GetResponse(HttpWebRequest request, DirectWebRequestOptions options) in c:\TeamCity\buildAgent\work\bf9e2ca68b75a334\src\DotNetOpenAuth\Messaging\UntrustedWebRequestHandler.cs:line 258
 at DotNetOpenAuth.OpenId.ChannelElements.OpenIdChannel.GetDirectResponse(HttpWebRequest webRequest) in c:\TeamCity\buildAgent\work\bf9e2ca68b75a334\src\DotNetOpenAuth\OpenId\ChannelElements\OpenIdChannel.cs:line 277
 at DotNetOpenAuth.Messaging.Channel.RequestCore(IDirectedProtocolMessage request) in c:\TeamCity\buildAgent\work\bf9e2ca68b75a334\src\DotNetOpenAuth\Messaging\Channel.cs:line 542
 at DotNetOpenAuth.Messaging.Channel.Request(IDirectedProtocolMessage requestMessage) in c:\TeamCity\buildAgent\work\bf9e2ca68b75a334\src\DotNetOpenAuth\Messaging\Channel.cs:line 425
 at DotNetOpenAuth.Messaging.Channel.Request[TResponse](IDirectedProtocolMessage requestMessage) in c:\TeamCity\buildAgent\work\bf9e2ca68b75a334\src\DotNetOpenAuth\Messaging\Channel.cs:line 405
 at DotNetOpenAuth.OpenId.ChannelElements.SigningBindingElement.ProcessIncomingMessage(IProtocolMessage message) in c:\TeamCity\buildAgent\work\bf9e2ca68b75a334\src\DotNetOpenAuth\OpenId\ChannelElements\SigningBindingElement.cs:line 154
 at DotNetOpenAuth.Messaging.Channel.ProcessIncomingMessage(IProtocolMessage message) in c:\TeamCity\buildAgent\work\bf9e2ca68b75a334\src\DotNetOpenAuth\Messaging\Channel.cs:line 992
 at DotNetOpenAuth.OpenId.ChannelElements.OpenIdChannel.ProcessIncomingMessage(IProtocolMessage message) in c:\TeamCity\buildAgent\work\bf9e2ca68b75a334\src\DotNetOpenAuth\OpenId\ChannelElements\OpenIdChannel.cs:line 172
 at DotNetOpenAuth.Messaging.Channel.ReadFromRequest(HttpRequestInfo httpRequest) in c:\TeamCity\buildAgent\work\bf9e2ca68b75a334\src\DotNetOpenAuth\Messaging\Channel.cs:line 386
 at DotNetOpenAuth.OpenId.RelyingParty.OpenIdRelyingParty.GetResponse(HttpRequestInfo httpRequestInfo) in c:\TeamCity\buildAgent\work\bf9e2ca68b75a334\src\DotNetOpenAuth\OpenId\RelyingParty\OpenIdRelyingParty.cs:line 501

We have added a machines involved into the trusted machine list and turned off requires ssl but it makes no difference. We even tried removing out nonce store and using a stateless connection, but that didn't work either. We always get the same error.

We suspected the issue is arising as a result of the cluster node having a different IP from the load balancer when it connects to the OpenID Provider, but we're not sure.

Any ideas?