Reauthentication

Authgear provides an easy method to reauthenticate the end-users. You can use this as a security measure to protect sensitive operations.

Overview

Reauthentication in Authgear is built on top of the OIDC ID token. The ID token is a JWT.

Your sensitive operation server endpoint MUST require the ID token. When you receive the ID token, you MUST verify the signature of it. If the signature is valid, you can trust the claims inside the ID token.

The auth_time claim in the ID token tells when was the end-user last authenticated. You should check the auth_time claim to see if the end-user was authenticated recently enough.

The https://authgear.com/claims/user/can_reauthenticate claim in the ID token tells whether the end-user can be reauthenticated. If the value of this claim is false, then depending on your business needs, you can either allow the end-user to proceed, or forbid the end-user to perform sensitive operations. The flows are illustrated by the following diagrams.

Sequence diagram for end-user who CANNOT reauthenticate

Sequence diagram for end-user who CAN reauthenticate

SDK Integration

The following code snippets illustrate the interaction between the SDK and Authgear.

React Native

const biometricOptions = {
  ios: {
    localizedReason: 'Use biometric to authenticate',
    constraint: 'biometryCurrentSet' as const,
  },
  android: {
    title: 'Biometric Authentication',
    subtitle: 'Biometric authentication',
    description: 'Use biometric to authenticate',
    negativeButtonText: 'Cancel',
    constraint: ['BIOMETRIC_STRONG' as const],
    invalidatedByBiometricEnrollment: true,
  },
};

async function onClickPerformSensitiveOperation() {
  // Step 1: Refresh the ID token to ensure the claims are up-to-date.
  await authgear.refreshIDToken();

  // Step 2: Check if the end-user can be reauthenticated.
  const canReauthenticate = authgear.canReauthenticate();
  if (!canReauthenticate) {
    // Step 2.1: Depending on your business need, you may want to allow
    // the end-user to proceed.
    // Here we assume you want to proceed.

    const idTokenHint = authgear.getIDTokenHint();

    // Step 2.2: Call the sensitive endpoint with the ID token.
    // It is still required to pass the ID token to the endpoint so that
    // the endpoint can know the end-user CANNOT be reauthenticated.
    return callMySensitiveEndpoint(idTokenHint);
  }

  // Step 3: The end-user can be reauthenticated.
  // If your app supports biometric authentication, you can pass
  // the biometric options to reauthenticate.
  // If biometric is enabled for the current user, it will be used instead.
  await authgear.reauthenticate({
    redirectURI: THE_REDIRECT_URI,
  }, biometricOptions);

  // Step 4: If we reach here, the reauthentication was done.
  // The ID token have up-to-date auth_time claim.
  const idTokenHint = authgear.getIDTokenHint();

  return callMySensitiveEndpoint(idTokenHint);
}

Flutter

final ios = BiometricOptionsIOS(
    localizedReason: "Use biometric to authenticate",
    constraint: BiometricAccessConstraintIOS.biometryAny,
);
final android = BiometricOptionsAndroid(
    title: "Biometric Authentication",
    subtitle: "Biometric authentication",
    description: "Use biometric to authenticate",
    negativeButtonText: "Cancel",
    constraint: [BiometricAccessConstraintAndroid.biometricStrong],
    invalidatedByBiometricEnrollment: false,
);

Future<void> onClickPerformSensitiveOperation() async {
    // Step 1: Refresh the ID token to ensure the claims are up-to-date.
    await authgear.refreshIDToken();

    // Step 2: Check if the end-user can be reauthenticated.
    final canReauthenticate = authgear.canReauthenticate;
    if (!canReauthenticate) {
        // Step 2.1: Depending on your business need, you may want to allow
        // the end-user to proceed.
        // Here we assume you want to proceed.
        final idTokenHint = authgear.idTokenHint;

        // Step 2.2: Call the sensitive endpoint with the ID token.
        // It is still required to pass the ID token to the endpoint so that
        // the endpoint can know the end-user CANNOT be reauthenticated.
        return callMySensitiveEndpoint(idTokenHint);
    }

    // Step 3: The end-user can be reauthenticated.
    // If your app supports biometric authentication, you can pass
    // the biometric options to reauthenticate.
    // If biometric is enabled for the current user, it will be used instead.
    await authgear.reauthenticate(
        redirectURI: THE_REDIRECT_URI,
        biometricIOS: ios,
        biometricAndroid: android,
    );

    // Step 4: If we reach here, the reauthentication was done.
    // The ID token have up-to-date auth_time claim.
    final idTokenHint = authgear.idTokenHint;

    return callMySensitiveEndpoint(idTokenHint);
}

Xamarin

var ios = new BiometricOptionsIos
{
    LocalizedReason = "Use biometric to authenticate",
    AccessConstraint = BiometricAccessConstraintIos.BiometricAny,
};
var android = new BiometricOptionsAndroid
{
    Title = "Biometric Authentication",
    Subtitle = "Biometric authentication",
    Description = "Use biometric to authenticate",
    NegativeButtonText = "Cancel",
    AccessConstraint = BiometricAccessConstraintAndroid.BiometricOnly,
    InvalidatedByBiometricEnrollment = false,
};

async void OnPerformSensitiveOperationClicked(object sender, EventArgs args)
{
    // Step 1: Refresh the ID token to ensure the claims are up-to-date.
    await authgear.RefreshIdTokenAsync();

    // Step 2: Check if the end-user can be reauthenticated.
    var canReauthenticate = authgear.CanReauthenticate;
    if (!canReauthenticate)
    {
        // Step 2.1: Depending on your business need, you may want to allow
        // the end-user to proceed.
        // Here we assume you want to proceed.
        var idTokenHint = authgear.IdTokenHint;

        // Step 2.2: Call the sensitive endpoint with the ID token.
        // It is still required to pass the ID token to the endpoint so that
        // the endpoint can know the end-user CANNOT be reauthenticated.
        await CallMySensitiveEndpointAsync(idTokenHint);
        return;
    }

    // Step 3: The end-user can be reauthenticated.
    // If your app supports biometric authentication, you can pass
    // the biometric options to reauthenticate.
    // If biometric is enabled for the current user, it will be used instead.
    await authgear.ReauthenticateAsync(new ReauthenticateOptions
    {
        RedirectURI: THE_REDIRECT_URI,
    }, new BiometricOptions
    {
        Ios = ios,
        Android = android,
    });

    // Step 4: If we reach here, the reauthentication was done.
    // The ID token have up-to-date auth_time claim.
    var idTokenHint = authgear.IdTokenHint;
    await CallMySensitiveEndpointAsync(idTokenHint);
}

Web

async function onClickPerformSensitiveOperation() {
  // Step 1: Refresh the ID token to ensure the claims are up-to-date.
  await authgear.refreshIDToken();

  // Step 2: Check if the end-user can be reauthenticated.
  const canReauthenticate = authgear.canReauthenticate();
  if (!canReauthenticate) {
    // Step 2.1: Depending on your business need, you may want to allow
    // the end-user to proceed.
    // Here we assume you want to proceed.

    const idTokenHint = authgear.getIDTokenHint();

    // Step 2.2: Call the sensitive endpoint with the ID token.
    // It is still required to pass the ID token to the endpoint so that
    // the endpoint can know the end-user CANNOT be reauthenticated.
    return callMySensitiveEndpoint(idTokenHint);
  }

  // Step 3: The end-user can be reauthenticated.
  // The end-user will be redirected to Authgear.
  // When the reauthentication finishes,
  // The end-user will be redirected back to the given redirect URI.
  await authgear.startReauthentication({
    redirectURI: THE_REDIRECT_URI
  });
}

// Suppose the following function is run when the end-user is redirected to
// the redirect URI
async function onRedirectAfterReauthentication() {
  // You HAVE to configure authgear again
  // because your website have been visited freshly.
  await authgear.finishReauthentication();
  await authgear.refreshIDToken();
  const idTokenHint = authgear.getIDTokenHint();
  return callMySensitiveEndpoint(idTokenHint);
}

iOS

func onClickPerformSensitiveOperation() {
    // Step 1: Refresh the ID token to ensure the claims are up-to-date.
    authgear.refreshIDToken() { result in
        switch result {
        case .success:
            // Step 2: Check if the end-user can be reauthenticated.
            let canReauthenticate = authgear.canReauthenticate
            if !canReauthenticate {
                // Step 2.1: Depending on your business need, you may want to allow
                // the end-user to proceed.
                // Here we assume you want to proceed.
                let idTokenHint = authgear.idTokenHint
                // Step 2.2: Call the sensitive endpoint with the ID token.
                // It is still required to pass the ID token to the endpoint
                // so that the endpoint can know the end-user CANNOT
                // be reauthenticated.
                callMySensitiveEndpoint(idTokenHint)
                return
            }

            // Step 3: The end-user can be reauthenticated.
            // By default biometric is used for reauthentication if it is enabled for the current user.
            // If you do not want biometric to be used, specify skipUsingBiometric: true
            authgear.reauthenticate(redirectURI: THE_REDIRECT_URI, skipUsingBiometric: false) { result in
                switch result {
                case .success:
                    // Step 4: If we reach here, the reauthentication was done.
                    // The ID token have up-to-date auth_time claim.
                    let idTokenHint = authgear.idTokenHint
                    callMySensitiveEndpoint(idTokenHint)
                    return
                case let .failure(error):
                    // Handle the error
                }
            }
        case let .failure(error):
            // Handle the error
        }
    }
}

Android

public void onClickPerformSensitiveOperation() {
    BiometricOptions biometricOptions = new BiometricOptions(
        activity, // FragmentActivity
        "Biometric authentication", // title
        "Biometric authentication", // subtitle
        "Use biometric to authenticate", // description
        "Cancel", // negativeButtonText
        ALLOWED, // allowedAuthenticators
        true // invalidatedByBiometricEnrollment
    );

    // Step 1: Refresh the ID token to ensure the claims are up-to-date.
    authgear.refreshIDToken(new OnRefreshIDTokenListener() {
        @Override
        public void onFailed(Throwable throwable) {
            // Handle error
        }
        @Override
        public void onFinished() {
            // Step 2: Check if the end-user can be reauthenticated.
            boolean canReauthenticate = authgear.getCanReauthenticate();
            if (!canReauthenticate) {
                // Step 2.1: Depending on your business need, you may want to allow
                // the end-user to proceed.
                // Here we assume you want to proceed.
                String idTokenHint = authgear.getIDTokenHint();
                // Step 2.2: Call the sensitive endpoint with the ID token.
                // It is still required to pass the ID token to the endpoint
                // so that the endpoint can know the end-user CANNOT
                // be reauthenticated.
                callMySensitiveEndpoint(idTokenHint);
                return;
            }

            // Step 3: The end-user can be reauthenticated.
            // If your app supports biometric authentication, you can pass
            // the biometric options to reauthenticate.
            // If biometric is enabled for the current user, it will be used.
            ReauthenticateOptions options =
                new ReauthenticateOptions(THE_REDIRECT_URI);
            authgear.reauthenticate(options, biometricOptions, new OnReauthenticateListener() {
                @Override
                public void onFailed(Throwable throwable) {
                    // Handle error
                }
                @Override
                public void onFinished(UserInfo userInfo) {
                    // Step 4: If we reach here, the reauthentication was done.
                    // The ID token have up-to-date auth_time claim.
                    String idTokenHint = authgear.getIDTokenHint();
                    callMySensitiveEndpoint(idTokenHint);
                    return;
                }
            });
        }
    });
}

Reauthenticate conditionally by the last authentication time

If the end-users in your application often perform a series of sensitive operation, it is annoying that they have to reauthenticate themselves repeatedly before every operation. To allow the end-users to skip reauthentication if they have just reauthenticated themselves recently, the SDK allows you to inspect the last authentication time of the end-user.

JavaScript

async function onClickPerformSensitiveOperation() {
  await authgear.refreshIDToken();
  // Before you trigger reauthentication, check authTime first.
  const authTime = authgear.getAuthTime();
  if (authTime != null) {
    const now = new Date();
    const timeDelta = now.getTime() - authTime.getTime();
    if (timeDelta < 5 * 60 * 1000 /* 5 minutes */) {
      const idTokenHint = authgear.getIDTokenHint();
      return callMySensitiveEndpoint(idTokenHint);
    }
  }

  // Otherwise trigger authentication.
}

iOS

func onClickPerformSensitiveOperation() {
    authgear.refreshIDToken() { result in
        switch result {
        case .success:
            // Before you trigger reauthentication, check authTime first.
            if let authTime = authgear.authTime {
                let now = Date()
                let timeDelta = now.timeIntervalSince(authTime)
                if timeDelta < 5 * 60 {
                    let idTokenHint = authgear.idTokenHint
                    callMySensitiveEndpoint(idTokenHint)
                    return
                }
            }
            // Otherwise trigger authentication.
        case let .failure(error):
            // Handle the error
        }
    }
}

Android

public void onClickPerformSensitiveOperation() {
    authgear.refreshIDToken(new OnRefreshIDTokenListener() {
        @Override
        public void onFailed(Throwable throwable) {
            // Handle error
        }
        @Override
        public void onFinished() {
            // Before you trigger reauthentication, check authTime first.
            Date authTime = authgear.getAuthTime();
            if (authTime != null) {
                Date now = new Date();
                long timedelta = now.getTime() - authTime.getTime();
                if (timedelta < 5 * 60 * 1000) {
                    String idTokenHint = authgear.getIDTokenHint();
                    callMySensitiveEndpoint(idTokenHint);
                    return;
                }
            }
            // Otherwise trigger authentication.
        }
    });
}

Xamarin

public async void OnPerformSensitiveOperationClicked(object sender, EventArgs args)
{
    await authgear.RefreshIdTokenAsync();
    var authTime = authgear.AuthTime;
    if (authTime != null)
    {
        var now = DateTimeOffset.UtcNow;
        var timedelta = now - authTime.Value;
        if (timedelta < TimeSpan.FromMinutes(5))
        {
            var idTokenHint = authgear.IdTokenHint;
            callMySensitiveEndpoint(idTokenHint);
            return;
        }
    }
}

Backend Integration

Finally in your backend, you have to verify the signature of the ID token, and then validate the claims inside.

Python

import json
from contextlib import closing
from urllib.request import urlopen
from datetime import datetime, timezone, timedelta

import jwt
from jwt import PyJWKClient

base_address = "https://<your_app_endpoint>"

def fetch_jwks_uri(base_address):
    doc_url = base_address + "/.well-known/openid-configuration"
    with closing(urlopen(doc_url)) as f:
        doc = json.load(f)
    jwks_uri = doc["jwks_uri"]
    if not jwks_uri:
        raise Exception('Failed to fetch jwks uri.')
    return jwks_uri

def my_endpoint():
    id_token = GET_ID_TOKEN_FROM_HTTP_REQUEST_SOMEHOW()
    try:
        jwks_uri = fetch_jwks_uri(base_address)
        # Reuse PyJWKClient for better performance
        jwks_client = PyJWKClient(jwks_uri)
        signing_key = jwks_client.get_signing_key_from_jwt(id_token)
        claims = jwt.decode(
            id_token,
            signing_key.key,
            algorithms=["RS256"],
            audience=base_address,
            options={"verify_exp": True},
        )
        auth_time = claims["auth_time"]
        dt = datetime.fromtimestamp(auth_time)
        now = datetime.utcnow()
        delta = now - dt
        if delta > timedelta(minutes=5):
            raise ValueError("auth_time is not recent enough")
    except:
        # Handle error
        raise

Go

package main

import (
    "context"
    "encoding/json"
    "fmt"
    "net/http"
    "time"

    "github.com/lestrrat-go/jwx/jwk"
    "github.com/lestrrat-go/jwx/jwt"
)

var (
    baseAddress = "https://<your_app_endpoint>"
)

type OIDCDiscoveryDocument struct {
    JWKSURI string `json:"jwks_uri"`
}

func FetchOIDCDiscoveryDocument(endpoint string) (*OIDCDiscoveryDocument, error) {
    resp, err := http.DefaultClient.Get(endpoint)
    if err != nil {
        return nil, err
    }
    defer resp.Body.Close()

    if resp.StatusCode != http.StatusOK {
        return nil, fmt.Errorf(
            "failed to fetch discovery document: unexpected status code: %d",
            resp.StatusCode,
        )
    }

    var document OIDCDiscoveryDocument
    err = json.NewDecoder(resp.Body).Decode(&document)
    if err != nil {
        return nil, err
    }
    return &document, nil
}

func FetchJWK(baseAddress string) (jwk.Set, error) {
    doc, err := FetchOIDCDiscoveryDocument(
        baseAddress + "/.well-known/openid-configuration",
    )
    if err != nil {
        return nil, err
    }

    set, err := jwk.Fetch(context.Background(), doc.JWKSURI)
    return set, err
}

func CheckIDToken(idToken string) error {
    // fetch jwks_uri from Authgear
    // you can cache the value of jwks to have better performance
    set, err := FetchJWK(baseAddress)
    if err != nil {
        return fmt.Errorf("failed to fetch JWK: %s", err)
    }

    // parse jwt token
    token, err := jwt.ParseString(idToken, jwt.WithKeySet(set))
    if err != nil {
        return fmt.Errorf("invalid token: %s", err)
    }

    // validate jwt token
    err = jwt.Validate(token,
        jwt.WithClock(jwt.ClockFunc(
            func() time.Time { return time.Now().UTC() },
        )),
        jwt.WithIssuer(baseAddress),
    )
    if err != nil {
        return fmt.Errorf("invalid token: %s", err)
    }

    authTimeAny, ok := token.Get("auth_time")
    if !ok {
        return fmt.Errorf("no auth_time")
    }

    authTimeUnix, ok := authTimeAny.(float64)
    if !ok {
        return fmt.Errorf("auth_time is not number")
    }

    authTime := time.Unix(int64(authTimeUnix), 0)
    now := time.Now().UTC()

    diff := now.Sub(authTime)
    if diff > 5*time.Minute {
        return fmt.Errorf("auth_time is not recent enough")
    }

    return nil
}