Firebase phone authentication has been used for driver and rider's authenticatioin proccess. It provides us with free phone authentication SMS which has been localized for many countries too.
Use your own Google account or register for a new one for this app. Then go to firebase console and Then click on add project to create a new project and fill the fields:
Enable phone authentication
After you log into Firebase choice firebase auth and enable Phone sign-in method. (Develop->Authentication->Setup Sign-In method->Phone->Enable->Save)
You will need to add two applications to dashboard for rider and driver app. To do so go to project settings. Then hit Add iOS app button. A dialog will be shown to you that you will need to select application Id and name of rider/driver here. Now you will receive a file named google-services.plist which you will need to add to driver/rider project as Firebase instructs on this screen too. Now repeat this section for the other app too. (rider or driver) After finishing this both of your driver and rider folder should have a file named google-services.plist in their folder.