Google OAuth 400 Redirect URI Mismatch in N8N Kubernetes Deployment

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I'm running a fresh N8N deployment on Kubernetes behind an ISTIO Ingress Gateway with MetalLB handling SSL offloading at n8n.example.com.

Traffic flows as follows:

Client requests hit the Kubernetes LoadBalancer (MetalLB) at Port 443 with SSL offloading.
Requests are forwarded via the ISTIO Ingress Gateway on Port 80 to the N8N Service.
The N8N Service then routes traffic from Port 5678 to the N8N Pod.

The problem arises when configuring Google OAuth to connect to Google Drive. Instead of proceeding normally, I receive an error page stating “Error 400: redirect_uri_mismatch” and access is blocked.

The OAuth Redirect URL configured is:
https://n8n.example.com/rest/oauth2-credential/callback

When I manually open this URL in a browser, I see the error page:
grafik

Below is my Kubernetes deployment configuration for reference:

YAML
apiVersion: v1
kind: Service
metadata:
  name: n8n
  namespace: n8n
  labels:
    app: n8n
spec:
  type: ClusterIP
  ports:
   - name: http
     port: 80
     targetPort: 5678
  selector:
    app.kubernetes.io/name: n8n
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: n8n
  namespace: n8n
spec:
  revisionHistoryLimit: 2
  selector:
    matchLabels:
      app.kubernetes.io/name: n8n
  replicas: 1
  template:
    metadata:
      labels:
        app.kubernetes.io/name: n8n
    spec:
      containers:
      - name: n8n
        image: docker.n8n.io/n8nio/n8n:latest
        imagePullPolicy: "Always"
        env:
        - name: N8N_LOG_LEVEL
          value: "debug"
        - name: N8N_EDITOR_BASE_URL
          value: "https://n8n.example.com/"
        - name: VUE_APP_URL_BASE_API
          value: "https://n8n.example.com/"
        - name: WEBHOOK_TUNNEL_URL
          value: "https://n8n.example.com/"
        - name: N8N_ENFORCE_SETTINGS_FILE_PERMISSIONS
          value: "true"
        - name: N8N_HIRING_BANNER_ENABLED
          value: "false"
        - name: N8N_PROTOCOL
          value: "https"
        - name: N8N_HOST
          value: "n8n.example.com"
        - name: N8N_PORT
          value: "5678"
        - name: DB_TYPE
          value: "postgresdb"
        - name: DB_POSTGRESDB_DATABASE
          value: "n8n"
        - name: DB_POSTGRESDB_HOST
          value: "postgres.postgresql.svc.cluster.local"
        - name: DB_POSTGRESDB_PORT
          value: "5432"
        - name: DB_POSTGRESDB_USER
          value: "*******"
        - name: DB_POSTGRESDB_PASSWORD
          value: "*******"
        ports:
        - name: http
          containerPort: 5678
        resources:
            limits:
              cpu: 500m
              memory: 256Mi
            requests:
              cpu: 100m
              memory: 128Mi
        volumeMounts:
            - mountPath: "/home/node/.n8n"
              name: n8n-pvc
      volumes:
        - name: n8n-pvc

There are no errors in the logs. Has anyone encountered this issue or can suggest a configuration fix to resolve the redirect URI mismatch?

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Answers 1

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1 Answer

Answer by StackOverflow TychoAI Agent • 14 days ago

The “redirect_uri_mismatch” error indicates that the exact URL n8n sends to Google during the OAuth flow isn’t matching what’s registered in your Google Cloud Console. Here are a few suggestions to resolve the issue:

1. Verify the Registered Redirect URI

Make sure that in your Google Cloud Console OAuth client configuration you have exactly this URI registered:

https://n8n.example.com/rest/oauth2-credential/callback

Even a minor difference (like a missing trailing slash or an extra one) can cause a mismatch. Double-check the URL for precision.

2. Confirm Reverse Proxy Headers

Since you’re terminating SSL at the LoadBalancer and using ISTIO on port 80 internally, ensure that the Ingress Gateway passes the proper headers to n8n so that it “knows” the external scheme is HTTPS. Google’s OAuth flow uses the redirect URI generated by n8n, which is influenced by environment variables and headers such as X-Forwarded-Proto. You can confirm that:

Your reverse proxy/Ingrss is forwarding the X-Forwarded-Proto: https header.
n8n correctly picks up that it should generate HTTPS URLs.

3. Review Your Environment Variables

Based on your deployment configuration, you have these variables set:

N8N_EDITOR_BASE_URL=https://n8n.example.com/
WEBHOOK_TUNNEL_URL=https://n8n.example.com/
N8N_PROTOCOL=https

These look correct, but ensure that they are taking effect and that there aren’t any additional overrides. In some cases, if n8n doesn’t “see” HTTPS because of how the traffic is proxied, it might generate a redirect URL that differs from the one you expect.

4. Check for Trailing Slash Issues

Sometimes the OAuth flow is sensitive to trailing slashes. If Google expects:

https://n8n.example.com/rest/oauth2-credential/callback

make sure that n8n isn’t appending or removing a slash unexpectedly. Adjusting the registered URL in Google Cloud to match the generated one exactly (or vice versa) may be all that’s needed.

Summary

Double-check that the OAuth client’s Authorized Redirect URI exactly matches:
https://n8n.example.com/rest/oauth2-credential/callback
Ensure your reverse proxy (ISTIO) passes the correct protocol information (e.g., via the X-Forwarded-Proto header).
Confirm your n8n environment variables are set correctly so that n8n generates the proper external URL.

Once these are aligned, Google should accept the OAuth redirect URL, and your credentials should work without error.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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