B2C single sign-on and sign-out work fine on localhost, but not in dev environment

Neil B 21 Reputation points

We have two ASP.Net Webforms sites, I'll just call them website1.mysites.com and website2.mysites.com. My local copies work perfectly - I log into website1, then click on a link to website2 that goes to, for example, website2/page1, and I'm logged in and can see everything I expect to see. I can also logout of either website and it successfully logs out of the other.

I've copied over everything to our 2 dev sites but none of this is working properly. I'll log into website1, click a link to go to website2/page1 but when I reach it I'm not logged in. However, if I go to the root of website2 after logging into website1 then it logs me in fine. Single sign-out also doesn't work - I'll logout out of one of the sites, but I'll stay logged into the other one.

I've added in the Redirect URIs for the dev sites. I've checked the that the client IDs and secrets are correct for each site too. I can't help but think that there's something simple I'm missing, but I just can't see it. Is there anything else I need to check / do?

Microsoft Entra External ID
Microsoft Entra External ID
A modern identity solution for securing access to customer, citizen and partner-facing apps and services. It is the converged platform of Azure AD External Identities B2B and B2C. Replaces Azure Active Directory External Identities.
2,639 questions
Microsoft Entra ID
Microsoft Entra ID
A Microsoft Entra identity service that provides identity management and access control capabilities. Replaces Azure Active Directory.
19,458 questions
{count} votes