Recently I was doing some custom development for SharePoint 2010 and came across the need to determine whether the identity claim of a user (in a claims-based web application, of course) mapped back to a Windows (Active Directory) account. The reason was if the user was logging in with a Windows account, I wanted to look up some information about them in Active Directory. Since I knew the lookup wouldn’t work for non-Windows claims users (for example, a user who logged in with Forms Authentication), I wanted to make the code smart enough to only attempt the lookup for users with Windows accounts.

I’ve included a code snippet below that shows the approach I took. Basically I retrieve the original issuer of a user’s identity claim and check whether the issuer was Windows (Active Directory). But the same approach can be used to check for other issuers as well.

using Microsoft.SharePoint;
using Microsoft.SharePoint.Administration.Claims;

// Note: 'userLoginName' is a string containing the value of the 'LoginName' property
// from an SPUser object. In a claims-enabled web app, this will be a string similar
// to "i:0#.w|CONTOSO\JohnSmith".

if (SPClaimProviderManager.IsEncodedClaim(userLoginName))
{
   SPClaim claim = SPClaimProviderManager.Local.DecodeClaim(userLoginName);
   if (SPOriginalIssuers.GetIssuerType(claim.OriginalIssuer) == SPOriginalIssuerType.Windows)
   {
      // User identity claim maps back to a Windows/AD account.
      // Now I can use 'claim.Value' to grab the account name ("DOMAIN\Username")
      // and do something with it.

      // Note: SPClaimProviderManager.Local.ConvertClaimToIdentifier() could also be used
      // to get the account name from the claim, but in the case of a Windows-issued
      // identity claim it'll return the same string as the 'Value' property of the
      // SPClaim object.
   }
}

SPOriginalIssuerType is an enumeration that contains the following values:

• ClaimsProvider
• Forms
• SecurityTokenService
• TrustedProvider
• Unknown
• Windows

Hopefully this will get you started down the right path. Happy claims coding!