We implemented the Okta Umbraco integration via this tutorial:

https://effect.nz/our-thoughts/november-2021/umbraco-and-okta-integration/

It does the login seemingly correctly, as can be seen by the event logging in the Okta application control panel - however when it redirects back to Umbraco we get this error

"Sequence contains more than one element"

[InvalidOperationException: Sequence contains more than one element]
   System.Linq.Enumerable.SingleOrDefault(IEnumerable`1 source) +504
   Microsoft.Owin.Security.<AuthenticateAsync>d__20.MoveNext() in /_/src/Microsoft.Owin/Security/AuthenticationManager.cs:156 
etc etc

On this Stack Overflow post (https://stackoverflow.com/questions/27101402/sequence-contains-more-than-one-element-microsoft-owin-security-authenticationma) they seem to point at their being two authenticated "objects" which is causing the exception in the MS code at this point:

public async Task<AuthenticateResult> AuthenticateAsync(string authenticationType)
{
  IEnumerable<AuthenticateResult> source = await this.AuthenticateAsync(new string[] { authenticationType });
  return source.SingleOrDefault<AuthenticateResult>(); //<== this line throws because there are two  
}

Can anyone shine a light on what might be happening?

Thanks, Marshall