IIS Reverse Proxy with OpenIdConnect going to wrong Identity provider - azure-active-directory

Question

OpenIdConnect (Azure) Settings
// COOKIES: Tells it to use cookies for authentication.
app.SetDefaultSignInAsAuthenticationType(CookieAuthenticationDefaults.AuthenticationType);
app.UseCookieAuthentication(new CookieAuthenticationOptions()
{
CookieManager = new SystemWebCookieManager()
});
// OPEN-ID: Authenticate via Azure AD using OpenIdConnect.
//https://azure.microsoft.com/en-us/resources/samples/active-directory-dotnet-webapp-webapi-openidconnect/
app.UseOpenIdConnectAuthentication(new OpenIdConnectAuthenticationOptions()
{
ClientId = ClientID,
Authority = Authority,
PostLogoutRedirectUri = PostLogoutRedirectUri,
Notifications = new OpenIdConnectAuthenticationNotifications()
{
AuthenticationFailed = PrincipalService.OnAzureAuthenticationFailure,
// REFERENCE: https://russellyoung.net/2015/09/05/mvc-role-based-authorization-with-azure-active-directory-aad/
AuthorizationCodeReceived = (AuthorizationCodeReceivedNotification notification) =>
{
var username = notification.AuthenticationTicket.Identity.Name.Split('#').LastOrDefault();
Logger.Log(Level.Auth, "Azure login success! Username: '" + username + "'.");
return Task.FromResult(0);
}
}
});
ARR Url Rewrite Settings
<rewrite>
<outboundRules>
<preConditions>
<preCondition name="ResponseIsHtml1">
<add input="{RESPONSE_CONTENT_TYPE}" pattern="^text/html" />
</preCondition>
</preConditions>
</outboundRules>
<rules>
<rule name="Secondary Server" stopProcessing="true">
<match url="(.*)" />
<conditions>
<add input="{CACHE_URL}" pattern="^(https?)://" />
</conditions>
<action type="Rewrite" url="https://qa2mobile.auntmillies.com/{R:1}" />
<serverVariables>
</serverVariables>
</rule>
</rules>
</rewrite>
Problem
Azure AD authentication works just fine normally, but once I setup a reverse-proxy it starts taking me to my own domain as if it's the identity provider.
e.g. https://my.domain.com/<guid>/oauth2/authorize?client_id=<guid>&etc
From this point, if I manually change my.domain.com to login.microsoftonline.com it'll log me in and proceed to work normally.
If I remove the reverse proxy and set the server up normally, it goes directly to login.microsoftonline.com instead of my domain.
What is causing this? I mean, obviously the reverse proxy, but how do I fix it without removing the reverse proxy?

Answer 1

What is causing this? I mean, obviously the reverse proxy, but how do I fix it without removing the reverse proxy?
As far as I know, if you use url rewirte rule in the web.config, it will rewrite all the request to the https://my.domain.com/ domain which is include the login.microsoftonline.com.
I suggest you could write a new rule which is used to match the /oauth2 request url to directly rediret to the login.microsoftonline.com instead of the https://my.domain.com/. Then it will work well.
More details, you could refer to below url rewrite rule.
<rewrite>
<rules>
<rule name="rule2" stopProcessing="true">
<match url="<talentid>/oauth2/(.*)" />
<action type="Redirect" url="https://login.microsoftonline.com/{R:0}" />
</rule>
<rule name="ReverseProxyInboundRule1" stopProcessing="true">
<match url="(.*)" />
<action type="Rewrite" url="https://<domain>.com/{R:1}" />
</rule>
</rules>
<outboundRules>
<preConditions>
<preCondition name="ResponseIsHtml1">
<add input="{RESPONSE_CONTENT_TYPE}" pattern="^text/html" />
</preCondition>
</preConditions>
</outboundRules>
</rewrite>