If you are using FomrsAuthentication against ActiveDirectory you might want to search if a User Id exist in Active Directory or not before taking certain action like creating new profile.
Here is a Code Snippet used to Check for existance of a User in Active Directory. Some of the setting are stored in web.config.
Note: IT is highly recommended that you do not store usernames or passwords in web.config unencrypted here for demonstration I have put them in clear text to connect to AD.
ConfigurationSettings.AppSettings are read from web.config and you can add your own app settings for those variables.
public bool IsUserExistInActiveDirectory(string UserId)
bool IsValidLoginName = false;
string domain = "LDAP://" + ConfigurationSettings.AppSettings["Domain"];
System.DirectoryServices.DirectoryEntry entry =
new DirectoryEntry(domain, ConfigurationSettings.AppSettings["ADServiceAccount"], ConfigurationSettings.AppSettings["ADServiceAccountPassword"],
DirectorySearcher adSearcher = new DirectorySearcher(entry);
adSearcher.SearchScope = SearchScope.Subtree;
adSearcher.Filter = "(&(objectClass=user)(samaccountname=" + UserId + "))";
SearchResult oResult = adSearcher.FindOne();
if ( oResult != null)
IsValidLoginName = true;