OAuth 2.0 overview in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is OAuth 2.0?

OAuth 2.0 is a protocol that allows apps to access user data from another service securely without sharing passwords. It works by giving apps limited access tokens instead of full credentials.

beginner

Name the four main roles in OAuth 2.0.

The four main roles are: Resource Owner (user), Client (app requesting access), Authorization Server (issues tokens), and Resource Server (hosts protected data).

beginner

What is an access token in OAuth 2.0?

An access token is a special key given to an app after the user approves access. The app uses this token to get data from the resource server without needing the user's password.

intermediate

Explain the Authorization Code Grant flow in OAuth 2.0.

In this flow, the app redirects the user to the authorization server to log in and approve access. Then, the app gets a code it can exchange for an access token. This keeps the user's password safe.

beginner

Why is OAuth 2.0 better than sharing passwords between apps?

OAuth 2.0 lets users give apps limited access without sharing passwords. This reduces risk if an app is hacked and lets users control what data apps can see or change.

Which OAuth 2.0 role is responsible for issuing access tokens?

A Authorization Server

B Resource Owner

C Client

D Resource Server

The Authorization Server issues access tokens after verifying the user's approval.

What does an access token allow a client to do?

A Change the user's password

B Access protected resources on behalf of the user

C Authenticate the user directly

D Delete the user's account

Access tokens let the client access protected data without needing the user's password.

In OAuth 2.0, who is the Resource Owner?

A The server issuing tokens

B The app requesting access

C The user who owns the data

D The database storing data

The Resource Owner is the user who controls the data and grants permission.

Which OAuth 2.0 flow involves exchanging a code for an access token?

A Resource Owner Password Credentials Grant

B Implicit Grant

C Client Credentials Grant

D Authorization Code Grant

The Authorization Code Grant flow uses a code that the client exchanges for an access token.

Why should apps use OAuth 2.0 instead of asking for user passwords?

A To improve security by not handling passwords directly

B To make users enter passwords more often

C To store passwords in the app

D To avoid using tokens

OAuth 2.0 improves security by letting apps use tokens instead of passwords.

Describe the main roles involved in OAuth 2.0 and their responsibilities.

Think about who owns data, who asks for access, who grants tokens, and who holds the data.

Explain how the Authorization Code Grant flow works step-by-step.

Focus on the code the app gets before the token and why this is safer.

Practice

1. What is the main purpose of OAuth 2.0 in REST APIs?

easy

A. To replace usernames with email addresses

B. To encrypt all data sent between client and server

C. To allow apps to access user data securely without sharing passwords

D. To speed up API response times

Solution

1. Step 1: Understand OAuth 2.0's role

   OAuth 2.0 is designed to let apps access user data safely without needing the user's password.

2. Step 2: Compare options to OAuth 2.0 purpose

   Only To allow apps to access user data securely without sharing passwords correctly describes this purpose. Options A, B, and D describe unrelated functions.

3. Final Answer:

   To allow apps to access user data securely without sharing passwords -> Option C

4. Quick Check:

   OAuth 2.0 = Secure data access without password sharing [OK]

Hint: OAuth 2.0 = safe access without password sharing [OK]

Common Mistakes:

• Confusing OAuth with encryption protocols
• Thinking OAuth replaces usernames
• Assuming OAuth speeds up APIs

2. Which of the following is the correct OAuth 2.0 flow step to get an access token?

easy

A. Client sends password directly to resource server

B. Client sends authorization code to the authorization server

C. Resource server sends access token to client without request

D. Client sends refresh token to user

Solution

1. Step 1: Identify OAuth 2.0 token exchange step

   The client sends the authorization code to the authorization server to exchange it for an access token.

2. Step 2: Eliminate incorrect options

   Client sends password directly to resource server is wrong because passwords are not sent directly. Resource server sends access token to client without request is wrong because tokens are sent after request. Client sends refresh token to user is wrong because refresh tokens are sent to the authorization server, not the user.

3. Final Answer:

   Client sends authorization code to the authorization server -> Option B

4. Quick Check:

   Authorization code sent to server = Step to get access token [OK]

Hint: Authorization code sent to server to get token [OK]

Common Mistakes:

• Sending password instead of authorization code
• Expecting tokens without request
• Confusing refresh token recipient

3. Given this OAuth 2.0 flow snippet:

1. Client requests authorization code
2. User grants permission
3. Client receives authorization code
4. Client sends authorization code to token endpoint
5. Token endpoint returns access token

What is the output after step 5?

medium

A. Client has an access token to access protected resources

B. Client has the user's password

C. Client can directly access user data without token

D. Client must request authorization code again

Solution

1. Step 1: Follow OAuth 2.0 flow steps

   After step 5, the client receives an access token from the token endpoint.

2. Step 2: Understand access token purpose

   The access token lets the client access protected user data securely without needing the password.

3. Final Answer:

   Client has an access token to access protected resources -> Option A

4. Quick Check:

   Access token received = Access to resources [OK]

Hint: Access token means access granted to resources [OK]

Common Mistakes:

• Thinking client gets user password
• Assuming token is not needed for access
• Believing authorization code must be requested again

4. Identify the error in this OAuth 2.0 flow:

Client sends access token directly to user
User sends authorization code to resource server

medium

A. Access token should be sent to resource server, not user

B. Authorization code should be sent to client, not user

C. Client should never send tokens at all

D. User should send access token to authorization server

Solution

1. Step 1: Analyze token flow roles

   Access tokens are meant for the resource server to verify access, not for the user.

2. Step 2: Check authorization code flow

   The authorization code is sent from user to client, not to the resource server.

3. Final Answer:

   Access token should be sent to resource server, not user -> Option A

4. Quick Check:

   Access token destination = Resource server [OK]

Hint: Access token goes to resource server, not user [OK]

Common Mistakes:

• Sending access token to user instead of server
• Confusing authorization code recipient
• Thinking client never sends tokens

5. You want to build an app that accesses user data from a REST API using OAuth 2.0. Which combination correctly describes the roles and tokens involved?

hard

A. Client app sends refresh token to user to renew access token

B. User sends access token to client app, which then sends password to resource server

C. Resource server issues authorization code directly to client app without user consent

D. Client app uses authorization code to get access token from authorization server, then uses access token to access resource server

Solution

1. Step 1: Understand OAuth 2.0 roles

   The client app requests an authorization code from the authorization server after user consent.

2. Step 2: Token exchange and usage

   The client exchanges the authorization code for an access token, then uses it to access the resource server.

3. Final Answer:

   Client app uses authorization code to get access token from authorization server, then uses access token to access resource server -> Option D

4. Quick Check:

   Authorization code -> access token -> resource access [OK]

Hint: Authorization code to token, then token to resource [OK]

Common Mistakes:

• Thinking user sends tokens to client
• Assuming resource server issues codes without user
• Confusing refresh token flow