---
title: "What is a refresh token and how is it used?"  
description: "What is a refresh token and how is it used?"  
author: "ICSM Computer"  
published: 2025-06-08  
updated: 2025-06-08  
canonical: https://www.mindstick.com/interview/34217/what-is-a-refresh-token-and-how-is-it-used  
category: "c#"  
tags: ["c#", "authentication"]  
reading_time: 4 minutes  

---

# What is a refresh token and how is it used?

A **refresh token** is a special token used in **OAuth 2.0** and **OpenID Connect** that allows a client application to **obtain a new access token** **without requiring the user to log in again**.

## Why Refresh Tokens?

- **Access tokens expire** (e.g., in 1 hour) for security reasons.
- Instead of asking the user to authenticate again, the app uses a **refresh token** to get a new access token **silently**.
- This improves **UX** and **security**.

## Structure

- Refresh tokens are usually long, random strings (sometimes JWTs).
- Stored securely by the client.
- **Never sent to resource APIs** (only to the token endpoint).

## Typical Flow with Refresh Token

- **User logs in** using the Authorization Code flow.

```plaintext
{
  "access_token": "abc123",
  "refresh_token": "xyz789",
  "expires_in": 3600
}
```

- Server returns:
- After 1 hour (when access token expires):

   - Client sends:

```plaintext
POST /token
Content-Type: application/x-www-form-urlencoded

grant_type=refresh_token
refresh_token=xyz789
client_id=your-client-id
client_secret=your-client-secret
```

- Server responds with a **new access token** (and optionally new refresh token).

## Security Best Practices

| Rule | Description |
| --- | --- |
| Store securely | Save refresh tokens in a secure place (e.g., encrypted DB) |
| Use HTTPS | Always send refresh tokens over HTTPS |
| Rotate refresh tokens | Send a new refresh token each time you use it |
| Revoke on logout | Clear it on logout or server-side token revocation |
| Scope-limited | Refresh tokens should be scoped and client-bound |

## When Not to Use

For **public clients** (SPAs, JS in browser), refresh tokens can be risky unless you use **PKCE** and **Refresh Token Rotation**.

## Example (C# using IdentityModel library)

```cs
var client = new HttpClient();
var disco = await client.GetDiscoveryDocumentAsync("https://auth-server.com");

var tokenResponse = await client.RequestRefreshTokenAsync(new RefreshTokenRequest
{
    Address = disco.TokenEndpoint,
    ClientId = "client_id",
    ClientSecret = "client_secret",
    RefreshToken = "xyz789"
});

var newAccessToken = tokenResponse.AccessToken;
```

## Summary

| Feature | Description |
| --- | --- |
| Purpose | Get new access token without re-authenticating |
| Lifetime | Longer than access token (hours, days, or more) |
| Security | Must be stored securely; often issued only to trusted apps |
| Common With | Authorization Code Flow, OpenID Connect |

## Answers

### Answer by ICSM Computer

A **refresh token** is a special token used in **OAuth 2.0** and **OpenID Connect** that allows a client application to **obtain a new access token** **without requiring the user to log in again**.

## Why Refresh Tokens?

- **Access tokens expire** (e.g., in 1 hour) for security reasons.
- Instead of asking the user to authenticate again, the app uses a **refresh token** to get a new access token **silently**.
- This improves **UX** and **security**.

## Structure

- Refresh tokens are usually long, random strings (sometimes JWTs).
- Stored securely by the client.
- **Never sent to resource APIs** (only to the token endpoint).

## Typical Flow with Refresh Token

- **User logs in** using the Authorization Code flow.

```plaintext
{
  "access_token": "abc123",
  "refresh_token": "xyz789",
  "expires_in": 3600
}
```

- Server returns:
- After 1 hour (when access token expires):

   - Client sends:

```plaintext
POST /token
Content-Type: application/x-www-form-urlencoded

grant_type=refresh_token
refresh_token=xyz789
client_id=your-client-id
client_secret=your-client-secret
```

- Server responds with a **new access token** (and optionally new refresh token).

## Security Best Practices

| Rule | Description |
| --- | --- |
| Store securely | Save refresh tokens in a secure place (e.g., encrypted DB) |
| Use HTTPS | Always send refresh tokens over HTTPS |
| Rotate refresh tokens | Send a new refresh token each time you use it |
| Revoke on logout | Clear it on logout or server-side token revocation |
| Scope-limited | Refresh tokens should be scoped and client-bound |

## When Not to Use

For **public clients** (SPAs, JS in browser), refresh tokens can be risky unless you use **PKCE** and **Refresh Token Rotation**.

## Example (C# using IdentityModel library)

```cs
var client = new HttpClient();
var disco = await client.GetDiscoveryDocumentAsync("https://auth-server.com");

var tokenResponse = await client.RequestRefreshTokenAsync(new RefreshTokenRequest
{
    Address = disco.TokenEndpoint,
    ClientId = "client_id",
    ClientSecret = "client_secret",
    RefreshToken = "xyz789"
});

var newAccessToken = tokenResponse.AccessToken;
```

## Summary

| Feature | Description |
| --- | --- |
| Purpose | Get new access token without re-authenticating |
| Lifetime | Longer than access token (hours, days, or more) |
| Security | Must be stored securely; often issued only to trusted apps |
| Common With | Authorization Code Flow, OpenID Connect |


---

Original Source: https://www.mindstick.com/interview/34217/what-is-a-refresh-token-and-how-is-it-used

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