C# Language Authenticated SSL LDAP connection, SSL cert does not match reverse DNS

Example

Set up some constants for the server and authentication information. Assuming LDAPv3, but it's easy enough to change that.

// Authentication, and the name of the server.
private const string LDAPUser = "cn=example:app:mygroup:accts,ou=Applications,dc=example,dc=com";
private readonly char[] password = { 'p', 'a', 's', 's', 'w', 'o', 'r', 'd' };
private const string TargetServer = "ldap.example.com";

// Specific to your company. Might start "cn=manager" instead of "ou=people", for example.
private const string CompanyDN = "ou=people,dc=example,dc=com"; 

Actually create the connection with three parts: an LdapDirectoryIdentifier (the server), and NetworkCredentials.

// Configure server and port. LDAP w/ SSL, aka LDAPS, uses port 636.
// If you don't have SSL, don't give it the SSL port. 
LdapDirectoryIdentifier identifier = new LdapDirectoryIdentifier(TargetServer, 636);

// Configure network credentials (userid and password)
var secureString = new SecureString();
foreach (var character in password)
        secureString.AppendChar(character);
NetworkCredential creds = new NetworkCredential(LDAPUser, secureString);

// Actually create the connection
LdapConnection connection = new LdapConnection(identifier, creds)
{
    AuthType = AuthType.Basic, 
    SessionOptions =
    {
        ProtocolVersion = 3,
        SecureSocketLayer = true
    }
};

// Override SChannel reverse DNS lookup.
// This gets us past the "The LDAP server is unavailable." exception
// Could be 
//    connection.SessionOptions.VerifyServerCertificate += { return true; };
// but some certificate validation is probably good.
connection.SessionOptions.VerifyServerCertificate +=
    (sender, certificate) => certificate.Subject.Contains(string.Format("CN={0},", TargetServer));

Use the LDAP server, e.g. search for someone by userid for all objectClass values. The objectClass is present to demonstrates a compound search: The ampersand is the boolean "and" operator for the two query clauses.

 SearchRequest searchRequest = new SearchRequest(
        CompanyDN, 
        string.Format((&(objectClass=*)(uid={0})), uid), 
        SearchScope.Subtree,
        null
);

// Look at your results
foreach (SearchResultEntry entry in searchResponse.Entries) {
    // do something
}