Automatic authentication in Postman

postman-auth.js

/**
 * Ensures that we have a valid token before any request.
 * 
 * To use this, you need to edit the Collection
 * 1) select "Bearer Token" and provide `{{accessToken}}` as the Token, under Authorisation tab.
 * 2) copy this script into "Pre-request scripts"
 * 
 * Last, you need to define the following variables under the Environment
 *   baseUrl : API URL ie https://example.com/
 *   username: The username to connect with
 *   password: The password for the above username
 */ 
const tokenExists = pm.environment.get('accessToken') && pm.environment.get('expiresOn');
if (tokenExists) {
    const tokenExpired = pm.environment.get('expiresOn') <= (new Date()).getTime() - 30;
    if (tokenExpired) {
      // Token expired so we are renewing
      const refreshTokenRequest = {
        url: pm.environment.get('baseUrl') + '/api/session/token',
        method: 'POST',
        header: 'Content-Type:application/json',
        body: {
          mode: 'application/json',
          raw: JSON.stringify({
            refresh_token: pm.environment.get('refreshToken')
          })
        }
      };
      pm.sendRequest(refreshTokenRequest, (error, response) => {
        if (error !== null) {
          console.log(error);
          return;
        }

        const data = response.json();
        const expiresOn = new Date();
        expiresOn.setSeconds(expiresOn.getSeconds() + data.expires_in)
        pm.environment.set('expiresOn', expiresOn.getTime());
        pm.environment.set('accessToken', data.access_token);
      });     
    }    
} else {
  // Token not found so we are creating a new session
  const newTokenRequest = {
    url: pm.environment.get('baseUrl') + '/api/token',
    method: 'POST',
    header: 'Content-Type:application/json',
    body: {
      mode: 'application/json',
      raw: JSON.stringify({
          username: pm.environment.get('username'),
          password: pm.environment.get('password')
      })
    }
  };

  pm.sendRequest(newTokenRequest, (error, response) => {
    if (error !== null) {
      console.log(error);
      return;
    }

    const data = response.json();

    const expiresOn = new Date();
    expiresOn.setSeconds(expiresOn.getSeconds() + data.expires_in)
    pm.environment.set('expiresOn', expiresOn.getTime());
    pm.environment.set('accessToken', data.access_token);
    pm.environment.set('refreshToken', data.refresh_token);
  });  
}