How to use refresh token to get access token in fastapi?

@denis 

To use a refresh token to get a new access token in FastAPI, you can follow these steps:

1. Before using the refresh token, you first need to generate it when the access token expires. Usually, the refresh token is provided alongside the access token when a user logs in or authenticates.
2. Store the refresh token securely, as it will be used to generate a new access token when needed.
3. Create an endpoint in your FastAPI application that accepts the refresh token as a parameter and verifies its validity.
4. Use the refresh token to generate a new access token by performing the necessary authentication and authorization checks. This typically involves decoding the token, validating its expiration time, and verifying its signature.
5. If the refresh token is valid, generate a new access token using the same method as when a user logs in or authenticates. This could involve generating a JWT (JSON Web Token) with the appropriate payload and expiry time.
6. Return the new access token to the client so that they can use it for further requests.

Example code in FastAPI to use a refresh token to get a new access token:

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from fastapi import FastAPI

app = FastAPI()

@app.post("/refresh_token")
async def refresh_token(refresh_token: str):
    # Verify the refresh token
    if verify_refresh_token(refresh_token):
        # Generate a new access token
        new_access_token = generate_access_token()
        return {"access_token": new_access_token}
    else:
        return {"error": "Invalid refresh token"}

# Function to verify the refresh token
def verify_refresh_token(refresh_token):
    # Add your verification logic here
    return True

# Function to generate a new access token
def generate_access_token():
    # Add your token generation logic here
    return "new_access_token"

In this example, the /refresh_token endpoint is used to accept a refresh token and generate a new access token if the refresh token is valid. You need to implement the verify_refresh_token function to verify the refresh token and the generate_access_token function to generate a new access token.

Remember to secure your endpoint with proper authentication and authorization checks to prevent unauthorized access to the refresh token generation functionality.