Using Laravel 4.1.30 I got this following code which test a sign-in attempt via Auth.

//... more codes here ...

$auth = Auth::attempt(array(
    'email'     => Input::get('email'),
    'password'  => Input::get('password'),
    'active'    => 1
), $remember);

if ($auth) {
    //... more codes here ...
}

I like to implement a conditional value such as:

->active > 0

I am using the active (field) as a level of authentication for users signing in. Anything above 0 (zero) should satisfy the next condition.

How can it be done in one statement?

tl;dr

You can't do this within the array passed to Auth::attempt(), because in the framework it is hard coded to use equality comparison in the generated query.

Full review

Framework implementation

The attempt() function is implemented in Illuminate/Auth/Guard.php.

public function attempt(array $credentials = array(), $remember = false, $login = true)
{
    $this->fireAttemptEvent($credentials, $remember, $login);

    $this->lastAttempted = $user = $this->provider->retrieveByCredentials($credentials);

    // If an implementation of UserInterface was returned, we'll ask the provider
    // to validate the user against the given credentials, and if they are in
    // fact valid we'll log the users into the application and return true.
    if ($this->hasValidCredentials($user, $credentials))
    {
        if ($login) $this->login($user, $remember);

        return true;
    }

    return false;
}

Here you can see a call for $this->provider->retrieveByCredentials($credentials);. The retrieveByCredentials() function is implemented in Illuminate/Auth/DatabaseUserProvider.php.

public function retrieveByCredentials(array $credentials)
{
    // First we will add each credential element to the query as a where clause.
    // Then we can execute the query and, if we found a user, return it in a
    // generic "user" object that will be utilized by the Guard instances.
    $query = $this->conn->table($this->table);

    foreach ($credentials as $key => $value)
    {
        if ( ! str_contains($key, 'password'))
        {
            $query->where($key, $value);
        }
    }

    // Now we are ready to execute the query to see if we have an user matching
    // the given credentials. If not, we will just return nulls and indicate
    // that there are no matching users for these given credential arrays.
    $user = $query->first();

    if ( ! is_null($user))
    {
        return new GenericUser((array) $user);
    }
}

Here you can see that the array you pass to Auth::attempt() is processed in a foreach and every key-value pairs are added as a WHERE clause to the query. Because it done with a $query->where($key, $value); call, it is limited to equality comparison.

Possible solutions

A workaround would be to change this line to something like:

$query->where($key, $value['operator'], $value['value']);

Then you could restructure the array given to Auth::attempt().

$auth = Auth::attempt(array(
    'email' => array(
        'value'    => Input::get('email'),
        'operator' => '='
    ),
    'password' => array(
        'value'    => Input::get('password'),
        'operator' => '='
    ),
    'active' => array(
        'value'    => 0,
        'operator' => '>'
    )
), $remember);

The problem with this is that you have to override every other function that uses this array, so you end up with a custom solution. With this effort you could write your own authentication query or do a check on active after Auth::attempt().