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Selahaddin Osmanoglu
Selahaddin Osmanoglu

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Google Classroom API: Fetching Students with OAuth2

This guide shows how to allow a teacher to log into your app with Google OAuth, and then use their token to fetch student rosters from Google Classroom.

Google Cloud Setup

  1. Go to Google Cloud Console.
  2. Create a new project.
  3. Enable the Classroom API under APIs & Services → Library.
  4. Configure the OAuth Consent Screen:
    • Choose External.
    • Fill in app details.
    • Add scopes:
      • https://www.googleapis.com/auth/classroom.courses.readonly
      • https://www.googleapis.com/auth/classroom.rosters.readonly
    • Add test users.
  5. Create OAuth Client ID:
    • Go to APIs & Services → Credentials → Create Credentials → OAuth client ID.
    • Choose Web Application.
    • Add redirect URIs (e.g., http://localhost:3000/oauth2callback, https://myapp.com/oauth2callback).
    • Save Client ID and Client Secret.

OAuth 2.0 Flow

Step 1: Redirect Teacher to Google Login 

https://accounts.google.com/o/oauth2/v2/auth?
 client_id=YOUR_CLIENT_ID&
 redirect_uri=YOUR_REDIRECT_URI&
 response_type=code&
 scope=https://www.googleapis.com/auth/classroom.courses.readonly https://www.googleapis.com/auth/classroom.rosters.readonly&
 access_type=offline&
 prompt=consent
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  • access_type=offline → gives refresh tokens.
  • prompt=consent → forces consent screen.

Step 2: Teacher Grants Access

Google redirects to:

https://your-app.com/oauth2callback?code=AUTH_CODE
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Step 3: Exchange Code for Tokens 

POST https://oauth2.googleapis.com/token
Content-Type: application/x-www-form-urlencoded

code=AUTH_CODE
&client_id=YOUR_CLIENT_ID
&client_secret=YOUR_CLIENT_SECRET
&redirect_uri=YOUR_REDIRECT_URI
&grant_type=authorization_code
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Example response:

{
  "access_token": "ya29.a0AfH6SMA...",
  "expires_in": 3599,
  "refresh_token": "1//0gAbCdEfGhIjKlMn...",
  "scope": "https://www.googleapis.com/auth/classroom.courses.readonly https://www.googleapis.com/auth/classroom.rosters.readonly",
  "token_type": "Bearer"
}
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Step 4: Use Access Token

Add header:

Authorization: Bearer ACCESS_TOKEN
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Classroom API Calls

Get Teacher’s Courses 

GET https://classroom.googleapis.com/v1/courses
Authorization: Bearer ACCESS_TOKEN
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Example:

{
  "courses": [
    {
      "id": "123456789012",
      "name": "Algebra 1",
      "section": "Period 2",
      "descriptionHeading": "Algebra Basics",
      "ownerId": "me",
      "courseState": "ACTIVE"
    },
    {
      "id": "987654321098",
      "name": "History 101",
      "ownerId": "me",
      "courseState": "ACTIVE"
    }
  ]
}
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Get Students in a Course 

GET https://classroom.googleapis.com/v1/courses/{courseId}/students
Authorization: Bearer ACCESS_TOKEN
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Example:

{
  "students": [
    {
      "userId": "111111111111111111111",
      "profile": {
        "id": "111111111111111111111",
        "name": {
          "givenName": "Alice",
          "familyName": "Johnson",
          "fullName": "Alice Johnson"
        },
        "emailAddress": "alice@example.com",
        "photoUrl": "https://lh3.googleusercontent.com/a/default-user"
      }
    },
    {
      "userId": "222222222222222222222",
      "profile": {
        "id": "222222222222222222222",
        "name": {
          "givenName": "Bob",
          "familyName": "Smith",
          "fullName": "Bob Smith"
        },
        "emailAddress": "bob@example.com"
      }
    }
  ]
}
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Get a Single Student 

GET https://classroom.googleapis.com/v1/courses/{courseId}/students/{userId}
Authorization: Bearer ACCESS_TOKEN
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Example:

{
  "userId": "111111111111111111111",
  "profile": {
    "id": "111111111111111111111",
    "name": {
      "givenName": "Alice",
      "familyName": "Johnson",
      "fullName": "Alice Johnson"
    },
    "emailAddress": "alice@example.com"
  }
}
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Token Refresh

When the access token expires:

POST https://oauth2.googleapis.com/token
Content-Type: application/x-www-form-urlencoded

client_id=YOUR_CLIENT_ID
&client_secret=YOUR_CLIENT_SECRET
&refresh_token=REFRESH_TOKEN
&grant_type=refresh_token
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Example:

{
  "access_token": "ya29.a0AfH6SMAnewtoken...",
  "expires_in": 3599,
  "scope": "https://www.googleapis.com/auth/classroom.courses.readonly https://www.googleapis.com/auth/classroom.rosters.readonly",
  "token_type": "Bearer"
}
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✅ Summary

  • Create Cloud Project → Enable Classroom API → OAuth Client ID.
  • Redirect teacher to Google OAuth.
  • Exchange authorization code for tokens.
  • Use access token to call Classroom API.
  • Fetch courses, then students per course.
  • Store refresh tokens for long-term use.

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