actions.js

export function signInRequest(email, password) {
  return {
    type: '@auth/SIGN_IN_REQUEST',
    payload: { email, password },
  };
}

export function signInSuccess(token, user) {
  return {
    type: '@auth/SIGN_IN_SUCCESS',
    payload: { token, user },
  };
}

reducer.js

import produce from 'immer';

const INITIAL_STATE = {
  token: null,
  signed: false,
  loading: false,
};

export default function auth(state = INITIAL_STATE, action) {
  return produce(state, draft => {
    switch (action.type) {
      case '@auth/SIGN_IN_REQUEST': {
        draft.loading = true;
        break;
      }
      case '@auth/SIGN_IN_SUCCESS': {
        draft.token = action.payload.token;
        draft.signed = true;
        draft.loading = false;
        break;
      }
      case '@auth/SIGN_FAILURE': {
        draft.loading = false;
        break;
      }
      default:
    }
  });
}

sagas.js

import { Alert } from 'react-native';
import { takeLatest, call, put, all } from 'redux-saga/effects';

import { signInSuccess, signUpSuccess, signFailure } from './actions';

import api from '~/services/api';

export function* signIn({ payload }) {
  try {
    const { email, password } = payload;

    const response = yield call(api.post, '/sessions', {
      email,
      password,
    });

    const { token, user } = response.data;

    api.defaults.headers.Authorization = `Bearer ${token}`;

    yield put(signInSuccess(token, user));

  } catch (err) {
    Alert.alert(
      'Falha na autenticação',
      err.response
        ? err.response.data.message
        : 'Verifique os dados, tente novamente'
    );

    yield put(signFailure());
  }
}

export function setToken({ payload }) {
  if (!payload) return;

  const { token } = payload.auth;

  if (token) {
    api.defaults.headers.Authorization = `Bearer ${token}`;
  }
}

export default all([
  takeLatest('persist/REHYDRATE', setToken),
  takeLatest('@auth/SIGN_IN_REQUEST', signIn),
]);