Authorization code flow with PKCE

The Authorization code flow with Proof Key for Code Exchange (PKCE) is an OAuth 2.0 authorization method used to implement user authentication. This page provides an overview of the flow and explains how to implement it.

This flow is an extension of the original Authorization code flow with added security measures. To learn about the base Authorization code flow, go to Authorization code flow.

This is the recommended OAuth 2.0 flow for user authentication in client applications.

Proof Key for Code Exchange (PKCE)

Proof Key for Code Exchange is an extension of the OAuth 2.0 specification that adds an extra layer of security using a locally generated code_verifier and code_challenge. This ensures that the client that requests an access token is the same client that requested an authorization code. This prevents attackers from intercepting an authorization code returned from the authorization endpoint and using it to gain system access.

The general steps for the authorization code flow with PKCE are:

1. Client generates a random code_verifier and code_challenge locally using SHA256 encryption.

2. Client sends a request to the authorization endpoint that includes the code_challenge as well as a client_id and redirect_uri from OAuth credentials.

3. The application user signs in with an ArcGIS account. The authorization endpoint verifies the user identity and returns an authorization code.

4. Client uses the authorization_code and code_verifier, as well as the client_id and redirect_uri from OAuth credentials, to submit a request to the token endpoint. The token endpoint checks that the code_verifier aligns with the original code_challenge and issues an access token.

5. Client uses the access token to authorize requests to secure resources.

ArcGIS APIs and SDKs

Authorization code with Proof Key for Code Exchange (PKCE) is the default authorization flow used by all ArcGIS APIs and Maps SDKs. To learn how to implement this flow using an ArcGIS API,

Manual implementation

The remainder of this page shows how to manually implement user authentication without using an ArcGIS API or Maps SDK. Instead, authentication is implemented by directly making HTTP requests to the proper REST API endpoints.

This sample is written in JavaScript, but can be implemented in any language. It adheres to the OAuth 2.0 specification for the Authorization code with Proof Key for Code Exchange (PKCE) flow.

Create OAuth credentials

User authentication requires a set of OAuth credentials.

Configure authentication variables

1. Copy your client ID and chosen redirect URL from your OAuth credentials and include them in your app.

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               const clientId = '<YOUR_CLIENT_ID>';
               const redirectUri = '<YOUR_REDIRECT_URL>';
   
               let session = null;
               let map = null;
               const signInButton = document.getElementById('sign-in');
               const signOutButton = document.getElementById('sign-out');
   

Generate a code verifier and challenge

1. Use language-specific libraries to generate a code verifier. This string is required in the "Authorization code with PKCE" flow, and will be sent to the token endpoint to request an access token.

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               const dec2hex = (dec) => {
                   return ('0' + dec.toString(16)).substr(-2)
               }
               const generateRandomString = () => {
                   var array = new Uint32Array(56/2);
                   window.crypto.getRandomValues(array);
                   return Array.from(array, dec2hex).join('');
               }
   
               const codeVerifier = generateRandomString();
   
   

2. Generate a code challenge, a base64 SHA256 encrypted version of the code verifier. This string will be sent to the authorization endpoint to obtain an authorization code.

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               const dec2hex = (dec) => {
                   return ('0' + dec.toString(16)).substr(-2)
               }
               const generateRandomString = () => {
                   var array = new Uint32Array(56/2);
                   window.crypto.getRandomValues(array);
                   return Array.from(array, dec2hex).join('');
               }
   
               const challengeFromVerifier = async (verifier) => {
                   // Generate SHA256 buffer
                   const encoder = new TextEncoder();
                   const data = encoder.encode(verifier);
                   const sha256 = await window.crypto.subtle.digest('SHA-256', data);
                   // Encode SHA256 as base 64
                   var str = "";
                   var bytes = new Uint8Array(sha256);
                   var len = bytes.byteLength;
                   for (var i = 0; i < len; i++) {
                       str += String.fromCharCode(bytes[i]);
                   }
                   const challenge = btoa(str)
                       .replace(/\+/g, "-")
                       .replace(/\//g, "_")
                       .replace(/=+$/, "");
                   return challenge;
               }
   
               const codeVerifier = generateRandomString();
   
               const codeChallenge = await challengeFromVerifier(codeVerifier);
   

Request an authorization code

1. Format a GET request to the authorization endpoint. Include your client_id, redirect_uri, and code_challenge.

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               const authorizationEndpoint = 'https://www.arcgis.com/sharing/rest/oauth2/authorize'+
               '?client_id=' + clientId +
               '&code_challenge=' + codeChallenge +
               '&code_challenge_method=S256' +
               '&redirect_uri=' + window.encodeURIComponent(redirectUri)+
               '&response_type=code'+
               '&expiration=20160';
   
   

2. When the user clicks 'sign in', open the authorization endpoint in a new window.

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               const authorizationEndpoint = 'https://www.arcgis.com/sharing/rest/oauth2/authorize'+
               '?client_id=' + clientId +
               '&code_challenge=' + codeChallenge +
               '&code_challenge_method=S256' +
               '&redirect_uri=' + window.encodeURIComponent(redirectUri)+
               '&response_type=code'+
               '&expiration=20160';
   
               signInButton.addEventListener('click', () => window.open(authorizationEndpoint, 'oauth-window', 'height=400,width=600,menubar=no,location=yes,resizable=yes,scrollbars=yes,status=yes'));
   

Create a callback

1. Create a callback function in index.html that will receive the authorization code.

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               const oauthCallback = (authorizationCode) => {
   
               }
               window.oauthCallback = oauthCallback; //required due to the module scope of this script
   

2. Create a new HTML page at the location of your redirect URI. When a user successfully authenticates at the authorization endpoint, they will be redirected to this page.

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   <!DOCTYPE html>
     <head>
       <title>ArcGIS user authentication OAuth 2.0 callback (vanilla JS)</title>
     </head>
     <body>
       <script type="module">
   
       </script>
     </body>
   </html>

3. Access the authorization code returned from the endpoint. It is found in the search parameter of the URL. Pass the code to the callback function created in index.html.

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   <!DOCTYPE html>
     <head>
       <title>ArcGIS user authentication OAuth 2.0 callback (vanilla JS)</title>
     </head>
     <body>
       <script type="module">
   
           const match = (window.location.search) ? window.location.search.match(/\?code=([^&]+)/) : false;
           // if we found an authorization code in the URL, pass the token up to a global function in index.html
           if(match[1]) {
               window.opener.oauthCallback(match[1]);
           }
           window.close();
   
       </script>
     </body>
   </html>

Request an access token

1. Find the URL of the token endpoint for your portal service. For ArcGIS Online users, the token endpoint is https://www.arcgis.com/sharing/rest/oauth2/token.

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               const oauthCallback = (authorizationCode) => {
   
                   const tokenEndpoint = 'https://www.arcgis.com/sharing/rest/oauth2/token';
   
               }
               window.oauthCallback = oauthCallback; //required due to the module scope of this script
   

2. Submit an HTTP request to the token endpoint to request an access token. Include your authorization_code, client_id, redirect_uri, and code_verifier to create a valid request, and set the grant_type as authorization_code.

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               const oauthCallback = (authorizationCode) => {
   
                   const tokenEndpoint = 'https://www.arcgis.com/sharing/rest/oauth2/token';
   
                   fetch(tokenEndpoint, {
                       method:'POST',
                       body: JSON.stringify({
                           client_id:clientId,
                           grant_type:'authorization_code',
                           code:authorizationCode,
                           redirect_uri:redirectUri,
                           code_verifier:codeVerifier
                       }),
                       headers: {
                           "Content-type": "application/json; charset=UTF-8"
                       }
                   })
   
               }
               window.oauthCallback = oauthCallback; //required due to the module scope of this script
   

3. Access the response from the endpoint. If the request was valid, the response will contain an access_token, refresh_token, username, and other session information.

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               const oauthCallback = (authorizationCode) => {
   
                   const tokenEndpoint = 'https://www.arcgis.com/sharing/rest/oauth2/token';
   
                   fetch(tokenEndpoint, {
                       method:'POST',
                       body: JSON.stringify({
                           client_id:clientId,
                           grant_type:'authorization_code',
                           code:authorizationCode,
                           redirect_uri:redirectUri,
                           code_verifier:codeVerifier
                       }),
                       headers: {
                           "Content-type": "application/json; charset=UTF-8"
                       }
                   })
   
                   .then(response => response.json()).then(newSession => {
                       updateSession(newSession);
                       initApp(newSession);
                   })
   
               }
               window.oauthCallback = oauthCallback; //required due to the module scope of this script
   

Serialize session info

1. Serialize the session information from the token endpoint and add it to local storage to make the session persistent across page refreshes.

   index.html

   Use dark colors for code blocksCopy

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               const updateSession = (sessionInfo) => {
                   const userInfo = document.getElementById('user-info');
   
                   if (!sessionInfo) {
                       localStorage.removeItem("__ARCGIS_USER_SESSION__");
                       session = null;
   
                       destroyApp();
   
                       // signed out sidebar state
                       userInfo.classList.add('hide');
                       userInfo.innerHTML = ``;
                       signOutButton.classList.add('hide');
                       signInButton.classList.remove('hide');
                   }
   
                   else {
                       session = sessionInfo;
                       localStorage.setItem("__ARCGIS_USER_SESSION__", JSON.stringify(session));
   
                       // signed in sidebar state
                       userInfo.classList.remove('hide');
                       userInfo.innerHTML = `Welcome, ${sessionInfo.username}.`;
                       signOutButton.classList.remove('hide');
                       signInButton.classList.add('hide');
                   }
   
               }