Function generate_refresh_token 

pub fn generate_refresh_token(
    user_id: &str,
    username: &str,
) -> Result<String, Box<dyn Error>>

Generates a new refresh token for a user.

Creates a JWT refresh token with the user’s ID and username. The token is signed using the configured JWT_SECRET and expires after JWT_REFRESH_DAYS days. Refresh tokens are long-lived and used to obtain new access tokens without re-authentication.

Arguments

• user_id - The unique identifier of the user.
• username - The username of the user.

Returns

• Ok(String) - The encoded JWT token string.
• Err(Box<dyn Error>) - If token encoding fails or config is not initialized.

Errors

Returns an error if:

• JWT encoding fails (invalid secret or configuration)
• The configured JWT secret is missing or invalid
• Config has not been initialized via Config::load()

Example

use crate::utility::jwt;

let token = jwt::generate_refresh_token("user123", "john_doe")
    .expect("Failed to generate token");
println!("Refresh token: {}", token);