Task: Authenticate a user in a workflow with openid connect

n8n workflow JSON:
{"id":"zeyTmqqmXaQIFWzV","meta":{"instanceId":"11f0bca80fdd47e21bd156f4266eada6e64a6bc4c37f34dc8ae14ccf768e9285"},"name":"OIDC client workflow","tags":[],"nodes":[{"id":"da0c6b83-9c8c-431b-beaa-66b5343b21c5","name":"Webhook","type":"n8n-nodes-base.webhook","position":[80,680],"webhookId":"891ad1cd-6a50-4a88-8789-95680c78f14c","parameters":{"path":"891ad1cd-6a50-4a88-8789-95680c78f14c","options":{},"responseMode":"responseNode"},"typeVersion":1},{"id":"5c9d4f59-7980-4bee-8df6-cf9ca3eccde1","name":"Code","type":"n8n-nodes-base.code","position":[520,680],"parameters":{"jsCode":"let myCookies = {};\nlet cookies = [];\n\ncookies = $input.item.json.headers.cookie.split(';')\nfor (item of cookies ) {\n  myCookies[item.split('=')[0].trim()]=item.split('=')[1].trim();\n}\n\nreturn myCookies;"},"typeVersion":2,"continueOnFail":true},{"id":"7867d061-c0e3-4359-90ac-a4536c948db2","name":"user info","type":"n8n-nodes-base.httpRequest","position":[1220,760],"parameters":{"url":"={{ $('Set variables : auth, token, userinfo, client id, scope').item.json.userinfo_endpoint }}","options":{},"sendHeaders":true,"headerParameters":{"parameters":[{"name":"Authorization","value":"=Bearer  {{ $json['access_token'] }}"}]}},"typeVersion":4.1,"continueOnFail":true},{"id":"df0e9896-0670-49cc-b7c6-140c234036b4","name":"send back login page","type":"n8n-nodes-base.respondToWebhook","position":[1900,980],"parameters":{"options":{},"respondWith":"text","responseBody":"={{ $json.html }}"},"typeVersion":1},{"id":"81f03c86-91fe-4960-b4c4-295252c7e8fc","name":"IF token is present","type":"n8n-nodes-base.if","position":[940,820],"parameters":{"conditions":{"number":[{"value1":"={{ $json['access_token'] }}","operation":"isNotEmpty"}]}},"typeVersion":1,"continueOnFail":true},{"id":"5e2f87bd-9c1f-4e87-82df-1b3b3e98cbdb","name":"Welcome page","type":"n8n-nodes-base.html","position":[1720,660],"parameters":{"html":"<!DOCTYPE html>\n\n<html>\n<head>\n  <meta charset=\"UTF-8\" />\n  <title>My HTML document</title>\n</head>\n<body>\n  <div class=\"container\">\n    <h1>Welcome {{$('user info').item.json.email }} </h1>\n  </div>\n</body>\n</html>\n\n<style>\n.container {\n  background-color: #ffffff;\n  text-align: center;\n  padding: 16px;\n  border-radius: 8px;\n}\n\nh1 {\n  color: #ff6d5a;\n  font-size: 24px;\n  font-weight: bold;\n  padding: 8px;\n}\n\nh2 {\n  color: #909399;\n  font-size: 18px;\n  font-weight: bold;\n  padding: 8px;\n}\n</style>\n"},"typeVersion":1},{"id":"c1448e12-4292-402b-bf9d-0ab555bbc734","name":"send back welcome page","type":"n8n-nodes-base.respondToWebhook","position":[1920,660],"parameters":{"options":{},"respondWith":"text","responseBody":"={{ $json.html }}"},"typeVersion":1},{"id":"8e64ab13-4f23-4c85-a625-c456910a9472","name":"IF user info ok","type":"n8n-nodes-base.if","position":[1400,760],"parameters":{"conditions":{"number":[{"value1":"={{ $json.email }}","operation":"isNotEmpty"}]}},"typeVersion":1,"continueOnFail":true},{"id":"a96b170f-fbd8-4061-9619-bf9877e85495","name":"login form","type":"n8n-nodes-base.html","position":[1700,980],"parameters":{"html":"<!-- Thanks to https://github.com/curityio/pkce-javascript-example/tree/master -->\n<!DOCTYPE html>\n<html lang=\"en\">\n  <head>\n    <meta charset=\"utf-8\">\n    <title>Login</title>\n  </head>\n  <style>\n.container {\n  background-color: #ffffff;\n  text-align: center;\n  padding: 16px;\n  border-radius: 8px;\n}\n\nh1 {\n  color: #ff6d5a;\n  font-size: 24px;\n  font-weight: bold;\n  padding: 8px;\n}\n\nh2 {\n  color: #909399;\n  font-size: 18px;\n  font-weight: bold;\n  padding: 8px;\n}\n</style>\n  <body>\n    <div id=\"result\"></div>\n    <script>\n    const authorizeEndpoint = \"{{ $('Set variables : auth, token, userinfo, client id, scope').item.json.auth_endpoint }}\";\n    const tokenEndpoint = \"{{ $('Set variables : auth, token, userinfo, client id, scope').item.json.token_endpoint }}\";\n    const clientId = \"{{ $('Set variables : auth, token, userinfo, client id, scope').item.json.client_id }}\";\n    const scope = \"{{ $('Set variables : auth, token, userinfo, client id, scope').item.json.scope }}\";\n    const usePKCE = {{ $('Set variables : auth, token, userinfo, client id, scope').item.json.PKCE }};\n        if (window.location.search) {\n            var args = new URLSearchParams(window.location.search);\n            var code = args.get(\"code\");\n\n            if (code) {\n                var xhr = new XMLHttpRequest();\n\n                xhr.onload = function() {\n                    var response = xhr.response;\n                    var message;\n\n                    if (xhr.status == 200) {\n                        message = \"Access Token: \" + response.access_token;\n                        document.cookie = \"access_token=\"+response.access_token;\n                        location.reload();\n                    }\n                    else {\n                        message = \"Error: \" + response.error_description + \" (\" + response.error + \")\";\n                    }\n\n                    document.getElementById(\"result\").innerHTML = message;\n                };\n                xhr.responseType = 'json';\n                xhr.open(\"POST\", tokenEndpoint, true);\n                xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');\n                xhr.send(new URLSearchParams({\n                    client_id: clientId,\n                    code_verifier: window.sessionStorage.getItem(\"code_verifier\"),\n                    grant_type: \"authorization_code\",\n                    redirect_uri: location.href.replace(location.search, ''),\n                    code: code\n                }));\n            }\n        }\n        async function generateCodeChallenge(codeVerifier) {\n            var digest = await crypto.subtle.digest(\"SHA-256\",\n                new TextEncoder().encode(codeVerifier));\n\n            return btoa(String.fromCharCode(...new Uint8Array(digest)))\n                .replace(/=/g, '').replace(/\\+/g, '-').replace(/\\//g, '_')\n        }\n\n        function generateRandomString(length) {\n            var text = \"\";\n            var possible = \"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789\";\n\n            for (var i = 0; i < length; i++) {\n                text += possible.charAt(Math.floor(Math.random() * possible.length));\n            }\n\n            return text;\n        }\n\n        if (!crypto.subtle) {\n            document.writeln('<p>' +\n                    '<b>WARNING:</b> The script will fall back to using plain code challenge as crypto is not available.</p>' +\n                    '<p>Javascript crypto services require that this site is served in a <a href=\"https://developer.mozilla.org/en-US/docs/Web/Security/Secure_Contexts\">secure context</a>; ' +\n                    'either from <b>(*.)localhost</b> or via <b>https</b>. </p>' +\n                    '<p> You can add an entry to /etc/hosts like \"127.0.0.1 public-test-client.localhost\" and reload the site from there, enable SSL using something like <a href=\"https://letsencrypt.org/\">letsencypt</a>, or refer to this <a href=\"https://stackoverflow.com/questions/46468104/how-to-use-subtlecrypto-in-chrome-window-crypto-subtle-is-undefined\">stackoverflow article</a> for more alternatives.</p>' +\n                    '<p>If Javascript crypto is available this message will disappear.</p>')\n        }\n\n      var codeVerifier = generateRandomString(64);\n\n            const challengeMethod = crypto.subtle ? \"S256\" : \"plain\"\n\n            Promise.resolve()\n                .then(() => {\n                    if (challengeMethod === 'S256') {\n                        return generateCodeChallenge(codeVerifier)\n                    } else {\n                        return codeVerifier\n                    }\n                })\n                .then(function(codeChallenge) {\n                    window.sessionStorage.setItem(\"code_verifier\", codeVerifier);\n\n                    var redirectUri = window.location.href.split('?')[0];\n                    var args = new URLSearchParams({\n                        response_type: \"code\",\n                        client_id: clientId,\n                        redirect_uri: redirectUri,\n                        scope: scope,\n                        state: generateRandomString(16)\n                    });\n                    if(usePKCE){\n                      args.append(\"code_challenge_method\", challengeMethod);\n                      args.append(\"code_challenge\", codeChallenge);\n                    }\n                window.location = authorizeEndpoint + \"?\" + args;\n            });\n    </script>\n  </body>\n</html>"},"typeVersion":1},{"id":"12395c64-1c9d-4801-8229-57d982e4243f","name":"Sticky Note","type":"n8n-nodes-base.stickyNote","position":[120,460],"parameters":{"width":510,"height":207,"content":"In this set, you have to retrieve from your identity provider : \n- auth url\n- token url\n- userinfo url\n- the client id you created for this flow\n- scopes to use, at least \"openid\" scope\nif you do not want to use PKCE, you have to fill : \n- client_secret\n- redirect_uri (which is the webhook uri)"},"typeVersion":1},{"id":"25e934b5-fcd6-49e1-bb33-955b5f3f34ca","name":"Sticky Note1","type":"n8n-nodes-base.stickyNote","position":[1640,480],"parameters":{"content":"At this point the user is authenticated, you have access to his profile from the user info result and you continue doing things"},"typeVersion":1},{"id":"9dab372a-3505-4be6-93bd-9e99fc71612c","name":"Sticky Note2","type":"n8n-nodes-base.stickyNote","position":[460,980],"parameters":{"width":776,"height":336,"content":"## Quick setup with Keycloak\n1. Open your Keycloak\n2. Go to `Realm settings` and opn `OpenID Endpoint Configuration`\n3. This will opene a new tab. Copy out the `authorization_endpoint`, `token_endpoint` and the `userinfo_endpoint` and add it to the `Set variables` node\n4. Go go `Clients` and click `Create client`. In there pick a name of choice.\n5. Go to the next step, `Capability config`, disable `Client authentication`. Only `Standard flow` should be checked.\n6. Go to the next step `Login settings`. In there copy the Webhook URL of this workflow into the `Valid redirect URIs` field\n7. Enter the clientID to the `Set variables` node\n\nNow you can activate the workflow and visit the webhook URL to test. You can find a more detailed setup guid in the description.\n"},"typeVersion":1},{"id":"6e3afc62-52a9-402a-bde9-e8798d0fd4f6","name":"Set variables : auth, token, userinfo, client id, scope","type":"n8n-nodes-base.set","position":[320,680],"parameters":{"values":{"string":[{"name":"auth_endpoint","value":"Your value here"},{"name":"token_endpoint","value":"Your value here"},{"name":"userinfo_endpoint","value":"Your value here"},{"name":"client_id","value":"name of your client"},{"name":"scope","value":"openid"},{"name":"redirect_uri","value":"webhook uri"},{"name":"client_secret","value":"secret of your client"}],"boolean":[{"name":"PKCE","value":true}]},"options":{}},"typeVersion":2},{"id":"2d54c64a-ae45-480f-923f-63d6cb3fcdfc","name":"IF we have code in URI and not in PKCE mode","type":"n8n-nodes-base.if","position":[700,680],"parameters":{"conditions":{"string":[{"value1":"={{ $('Webhook').item.json.query.code }}","operation":"isNotEmpty"}],"boolean":[{"value1":"={{ $('Set variables : auth, token, userinfo, client id, scope').item.json.PKCE }}"}]}},"typeVersion":1},{"id":"99c8fa5d-3173-4371-9742-6014eca6e7fe","name":"get access_token from /token endpoint with code","type":"n8n-nodes-base.httpRequest","position":[940,640],"parameters":{"url":"={{ $('Set variables : auth, token, userinfo, client id, scope').item.json.token_endpoint }}","method":"POST","options":{},"sendBody":true,"contentType":"form-urlencoded","bodyParameters":{"parameters":[{"name":"grant_type","value":"authorization_code"},{"name":"client_id","value":"={{ $('Set variables : auth, token, userinfo, client id, scope').item.json.client_id }}"},{"name":"client_secret","value":"={{ $('Set variables : auth, token, userinfo, client id, scope').item.json.client_secret }}"},{"name":"code","value":"={{ $('Webhook').item.json.query.code }}"},{"name":"redirect_uri","value":"={{ $('Set variables : auth, token, userinfo, client id, scope').item.json.redirect_uri }}"}]}},"typeVersion":4.1}],"active":true,"pinData":{},"settings":{"executionOrder":"v1"},"versionId":"d91ac207-6f83-42cd-9c9f-326b8c53c160","connections":{"Code":{"main":[[{"node":"IF we have code in URI and not in PKCE mode","type":"main","index":0}]]},"Webhook":{"main":[[{"node":"Set variables : auth, token, userinfo, client id, scope","type":"main","index":0}]]},"user info":{"main":[[{"node":"IF user info ok","type":"main","index":0}]]},"login form":{"main":[[{"node":"send back login page","type":"main","index":0}]]},"Welcome page":{"main":[[{"node":"send back welcome page","type":"main","index":0}]]},"IF user info ok":{"main":[[{"node":"Welcome page","type":"main","index":0}],[{"node":"login form","type":"main","index":0}]]},"IF token is present":{"main":[[{"node":"user info","type":"main","index":0}],[{"node":"login form","type":"main","index":0}]]},"IF we have code in URI and not in PKCE mode":{"main":[[{"node":"get access_token from /token endpoint with code","type":"main","index":0}],[{"node":"IF token is present","type":"main","index":0}]]},"get access_token from /token endpoint with code":{"main":[[{"node":"user info","type":"main","index":0}]]},"Set variables : auth, token, userinfo, client id, scope":{"main":[[{"node":"Code","type":"main","index":0}]]}}}