cakephp backend pour une app react native

Bonjour,
Je suis entrain de développer une application mobile en react native mais j'utilise cakephp 2 pour le backend.
je voudrais mettre en place un système de avec numero de télphone et mot de passe, J'ai un soucis quand j'envoie la requete ça ne marche pas.
Je me demande si c'est dû à la synthaxe des formulaire en cakephp? ou j'ai mal fait.
Besoin d'explication s'il vous plait.
Merci

voici mes code

component react native

import React from 'react';
import {StyleSheet, View, TextInput,Text, TouchableOpacity,Keyboard} from 'react-native';
import { getDoctors } from '../API/getDoctors';
class Formulaire extends React.Component {

  constructor(props){
    super(props);
      this.state={
        username:'',
        password:'',
    }
  }

  render() {
    return (

      <View style={styles.main_container}>

        <TextInput style={styles.inputPhone} 
        placeholder="N° de téléphone" 
        keyboardType="numeric"
        underlineColorAndroid='rgba(0,0,0,0)' 
        onChangeText={(username)=>this.setState({username})}/>

        <TextInput style={styles.inputPassword} 
        placeholder="Mot de passe" 
        keyboardType="default" 
        underlineColorAndroid='rgba(0,0,0,0)' 
        secureTextEntry={true}
        onChangeText={(password)=>this.setState({password})}/>

        <TouchableOpacity 
          style={styles.TouchConnect}
           onPress={this.Login}>
          <Text style={styles.input_text}>Se connecter</Text>
        </TouchableOpacity>

      </View>
    )

    }

    Login= () => {

      Keyboard.dismiss();
      fetch('https://www.test.com/mobile/users/loginApi/',{
        method:'POST',
        headers: {
        Accept: 'application/json',
          'Content-Type': 'application/json',
        },
        body: JSON.stringify({
          username: this.state.username,
          password: this.state.password,
        })
      })
      .then((response) => response.json())
        .then((responseJson) => {
          alert(JSON.stringify(responseJson));
          if(responseJson.status==='success'){
            this.props.navigation.navigate('welcome');
          }else{
            alert(JSON.stringify(responseJson));
          }
        })
        .catch((error)=>{
          console.error(error);
        })
    }
 }  

le code cakephp

public function loginApi(){

    $this->autoRender=false;
    $username= $this->data['username'];
    $this->request->data['User']['phone'] = $username;
    $this->Auth->authenticate['Form'] = array('fields' => array('username' => 'phone'));
     if(!$this->Auth->login()){ 
         $arrReturn=array();
         $arrReturn['status']='false';
         echo json_encode($arrReturn);
      }else {
           $userId=$this->Auth->User('id');
           if($this->Auth->User('role')=='patient'){
                $this->User->id=$userId;
                $this->User->saveField('lastlogin',date('y-m-d H:i:s'));
                $this->User->saveField('online','1');
                $user=$this->User->find('first',array('conditions'=>array('User.id'=>$userId),'fields'=>array('id','role','phone','username','filename','sexe','online','lastlogin')));
                     $arrReturn=array();
                     $arrReturn['status']='success';
                     $arrReturn['role']=$user['User']['role'];
                     $arrReturn['User']=$user['User'];
           echo json_encode($arrReturn);
           }else{
             $this->User->id=$userId;
             $this->User->saveField('lastlogin',date('y-m-d H:i:s'));
             $this->User->saveField('online','1');
            $user=$this->User->find('first',array('conditions'=>array('id'=>$userId),'fields'=>array('id','role','description','specialite','tag',
                  'online','phone','username','filename','online','lastlogin')));

                     $arrReturn=array();
                     $arrReturn['status']='success';
                     $arrReturn['User']=$user['User'];
                     echo json_encode($arrReturn);

           }
      }
}