When executing a get_session_key with postman as per the attachments I´ve got the following errors :
1- First time executed (lime_sessions table clean) => {"id":1,"result":null,"error":"unknown method or incorrect parameters"} (screen1)
2- Second time : {"id":1,"result":null,"error":"CDbCommand failed to execute the SQL statement: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '' for key 'PRIMARY'. The SQL statement executed was: INSERT INTO lime_sessions (id, expire, data) VALUES (:yp0, :yp1, :yp2). Bound with :yp0='', :yp1=1568076066, :yp2='admin'"} (screen2)
3- In the table lime_sessions I see there´s an entry without any id (null or blank). (see attachment screen3)

As per my understanding the server is not being able to create the random id and because of that the first time it creates an entry in the table with id null so the second time when it tries to create a second row it´s rejected because id is null too.
Is it possible yii is not running or not being installed properly?

public function get_session_key($username, $password, $plugin = 'Authdb')
{
    $username = (string) $username;
    $password = (string) $password;
    $loginResult = $this->_doLogin($username, $password, $plugin);
    if ($loginResult === true) {
        $this->_jumpStartSession($username);
        $sSessionKey = Yii::app()->securityManager->generateRandomString(32);
        $session = new Session;
        $session->id = $sSessionKey;

.......