---
title: "What are the different OAuth 2.0 grant types?"  
description: "What are the different OAuth 2.0 grant types?"  
author: "ICSM Computer"  
published: 2025-06-08  
updated: 2025-06-08  
canonical: https://www.mindstick.com/interview/34216/what-are-the-different-oauth-2-0-grant-types  
category: "c#"  
tags: ["c#", "authentication", "OAuth 2.0"]  
reading_time: 6 minutes  

---

# What are the different OAuth 2.0 grant types?

OAuth 2.0 defines **grant types** as different ways a client app can obtain an access token from the authorization server.

Each grant type is suited for different use cases — based on the type of client (web app, SPA, mobile, etc.) and level of trust.

## The 4 Main OAuth 2.0 Grant Types

| Grant Type | Use Case | Secure? |
| --- | --- | --- |
| **Authorization Code** | Web/mobile apps with a backend | Yes |
| **Client Credentials** | Server-to-server (no user involved) | Yes |
| **Password Grant** | Trusted apps asking for username/password | No (deprecated) |
| **Implicit Grant** | SPAs (JavaScript apps) — now discouraged | No (deprecated) |

### Authorization Code Grant (with PKCE)

> **Most secure and commonly used** for web & mobile apps.

#### Flow:

- User logs in and authorizes app.
- App receives a short-lived **authorization code**.
- App exchanges code (securely) for **access token** (and optionally refresh token).

**PKCE** (Proof Key for Code Exchange) adds extra security for mobile/SPAs.

#### Returns:

- `access_token`, `refresh_token`, `id_token` (if using OpenID Connect)

### Client Credentials Grant

> Used for **machine-to-machine** (M2M) communication, like a cron job or microservice.

#### Flow:

- App authenticates using its **client ID + secret** (no user).
- Gets an access token to call protected APIs.

#### Example:

```plaintext
POST /token
client_id=abc&client_secret=xyz&grant_type=client_credentials
```

### Password Grant (Resource Owner Password Credentials)

> The app collects the **username and password** of the user.

- Works only for **trusted first-party apps**.
- **Deprecated** due to security risk — user credentials are exposed to the app.

#### Flow:

- App sends `username`, `password`, and client credentials.
- Gets access token.

**Use With Caution.**

### Implicit Grant (Deprecated)

> Designed for **public clients** (e.g. JS apps in the browser) that can't securely store secrets.

- **Tokens are returned directly in the URL** (less secure).
- **Doesn't support refresh tokens**.
- Now replaced by **Authorization Code + PKCE**.

## Bonus: Other Specialized Grant Types

| Grant Type | Description |
| --- | --- |
| **Device Code Flow** | Used for devices without browser (e.g., Smart TVs, IoT devices). |
| **Refresh Token** | Not a grant type, but allows getting a new access token silently. |
| **JWT Bearer Grant** | Lets apps exchange a JWT for an access token. |

## Summary Chart

| Grant Type | User Involved | Secure Storage Required | Suitable For |
| --- | --- | --- | --- |
| Authorization Code | Yes | Yes | Web apps, mobile apps (via PKCE) |
| Client Credentials | No | Yes | Backend services, daemons |
| Password Grant | Yes | No | Trusted apps only (deprecated) |
| Implicit Grant | Yes | No | Deprecated — use PKCE instead |
| Device Code | Yes | No | Smart TVs, IoT, CLI |

Let me know if you’d like:

- A real **C# implementation** of any grant type
- Help picking the **right flow** for your app type
- Integration with **IdentityServer**, **Auth0**, or **Google/Facebook** auth

## Answers

### Answer by ICSM Computer

OAuth 2.0 defines **grant types** as different ways a client app can obtain an access token from the authorization server.

Each grant type is suited for different use cases — based on the type of client (web app, SPA, mobile, etc.) and level of trust.

## The 4 Main OAuth 2.0 Grant Types

| Grant Type | Use Case | Secure? |
| --- | --- | --- |
| **Authorization Code** | Web/mobile apps with a backend | Yes |
| **Client Credentials** | Server-to-server (no user involved) | Yes |
| **Password Grant** | Trusted apps asking for username/password | No (deprecated) |
| **Implicit Grant** | SPAs (JavaScript apps) — now discouraged | No (deprecated) |

### Authorization Code Grant (with PKCE)

> **Most secure and commonly used** for web & mobile apps.

#### Flow:

- User logs in and authorizes app.
- App receives a short-lived **authorization code**.
- App exchanges code (securely) for **access token** (and optionally refresh token).

**PKCE** (Proof Key for Code Exchange) adds extra security for mobile/SPAs.

#### Returns:

- `access_token`, `refresh_token`, `id_token` (if using OpenID Connect)

### Client Credentials Grant

> Used for **machine-to-machine** (M2M) communication, like a cron job or microservice.

#### Flow:

- App authenticates using its **client ID + secret** (no user).
- Gets an access token to call protected APIs.

#### Example:

```plaintext
POST /token
client_id=abc&client_secret=xyz&grant_type=client_credentials
```

### Password Grant (Resource Owner Password Credentials)

> The app collects the **username and password** of the user.

- Works only for **trusted first-party apps**.
- **Deprecated** due to security risk — user credentials are exposed to the app.

#### Flow:

- App sends `username`, `password`, and client credentials.
- Gets access token.

**Use With Caution.**

### Implicit Grant (Deprecated)

> Designed for **public clients** (e.g. JS apps in the browser) that can't securely store secrets.

- **Tokens are returned directly in the URL** (less secure).
- **Doesn't support refresh tokens**.
- Now replaced by **Authorization Code + PKCE**.

## Bonus: Other Specialized Grant Types

| Grant Type | Description |
| --- | --- |
| **Device Code Flow** | Used for devices without browser (e.g., Smart TVs, IoT devices). |
| **Refresh Token** | Not a grant type, but allows getting a new access token silently. |
| **JWT Bearer Grant** | Lets apps exchange a JWT for an access token. |

## Summary Chart

| Grant Type | User Involved | Secure Storage Required | Suitable For |
| --- | --- | --- | --- |
| Authorization Code | Yes | Yes | Web apps, mobile apps (via PKCE) |
| Client Credentials | No | Yes | Backend services, daemons |
| Password Grant | Yes | No | Trusted apps only (deprecated) |
| Implicit Grant | Yes | No | Deprecated — use PKCE instead |
| Device Code | Yes | No | Smart TVs, IoT, CLI |

Let me know if you’d like:

- A real **C# implementation** of any grant type
- Help picking the **right flow** for your app type
- Integration with **IdentityServer**, **Auth0**, or **Google/Facebook** auth


---

Original Source: https://www.mindstick.com/interview/34216/what-are-the-different-oauth-2-0-grant-types

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