How to specify the scope of Google API to get the birthday

Normally you will only get birthdays that have public visibility. To get private birthdays you need to use the https://www.googleapis.com/auth/user.birthday.read scope. See documentation for which scopes give you which data https://developers.google.com/people/v1/how-tos/authorizing#profile-scopes.

I just used and tested it using Try It. I tested it with all of the different scopes.

https://www.googleapis.com/auth/plus.login Know your basic profile info and list of people in your circles.

https://www.googleapis.com/auth/plus.me Know who you are on Google https://www.googleapis.com/auth/userinfo.email View your email address https://www.googleapis.com/auth/userinfo.profile View basic information about your account

It doesn't appear to matter you get back the birthday in all of the scopes. But what does matter is that the Users Birthday must be set to public in the Account. If it's set to anything else, your circles, only you, it's not listed. This appears to be true even when you are trying to see your own information. (Sending Me.)

Update and the year is 2018

The People api now returns the birthday of the current user

People.get However i suspect its linked to google+ so if the user hasn't filled it out you probably wont get info.

GET https://people.googleapis.com/v1/{resourceName=people/*}

Send Resournce name of people/me and birthdays personFields

{
  "resourceName": "people/117200475532672775346",
  "etag": "%EgQBBzcuGgwBAgMEBQYHCAkKCwwiDDQwaGhWYzc3cXJBPQ==",
  "birthdays": [
    {
      "metadata": {
        "primary": true,
        "source": {
          "type": "PROFILE",
          "id": "117200475532672775346"
        }
      },
      "date": {
        "month": 1,
        "day": 6
      }
    },
    {
      "metadata": {
        "source": {
          "type": "ACCOUNT",
          "id": "117200475532672775346"
        }
      },
      "date": {
        "year": 1971,
        "month": 1,
        "day": 6
      }
    }
  ]