The pre-request script to automatically renewal the JWT in Postman.

pre-request.js

function parseJwt (token) {
    const base64Url = token.split('.')[1];
    const base64 = base64Url.replace(/-/g, '+').replace(/_/g, '/');
    const jsonPayload = decodeURIComponent(atob(base64).split('').map((c) => {
        return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
    }).join(''));
    return JSON.parse(jsonPayload);
};

function isValidToken(token) {
    if (!token) return false;
    const { exp } = parseJwt(token);
    if (!exp) return false;
    return new Date().getTime() < new Date(exp * 1000).getTime();
}

function setJwtEnv(envKey, refreshFunc) {
    if (!envKey || !refreshFunc) return console.error("Argument is required");
    const latestToken = pm.environment.get(envKey);
    if (!isValidToken(latestToken)) {
        refreshFunc((token) => pm.environment.set(envKey, token));
    }
}

const req = {
    url: '[your-token-provider-url]',
    method: 'POST',
    header: {
        'Content-Type': 'application/json',
    },
    body: {
        mode: 'raw',
        raw: JSON.stringify({ email: '[your-email]', password: '[your-password]' })
    },
};

setJwtEnv("token", (setToken) => {
    pm.sendRequest(req, (error, response) => {
        if (error) return console.error(error);
        if (response.code !== 200) return console.error(response);
        const { id_token } = response.json();
        if (id_token) {
            setToken(id_token);
        }
    });
});