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Production APIs require a secure (HTTPS) origin — requests from http://localhost will fail CORS preflight checks. ngrok solves this by tunneling your local server through a public HTTPS URL in seconds.

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Step 1 — Install ngrok

brew install ngrok/ngrok/ngrok

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Step 2 — Get your Auth Token

  1. Go to ngrok.com and sign up (free)
  2. After login, go to Dashboard → Your Authtoken
  3. Copy the token — it looks like 2abc123XYZ_abcdefghijklmnop

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Step 3 — Add the token (one-time only)

ngrok config add-authtoken YOUR_TOKEN_HERE
You only need to do this once per machine.

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Step 4 — Start your app, then run ngrok

Start your local server first, then in a second terminal: 
ngrok http <YOUR_APP_PORT>
Replace <YOUR_APP_PORT> with the port your app runs on (e.g. 3000, 8000, 8080). ngrok will show output like: 
Forwarding   https://xxxx-xx-xx-xx.ngrok-free.app -> http://localhost:<YOUR_APP_PORT>
Open that https:// URL in any browser, on any device — it works and satisfies CORS requirements for production APIs.

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Stop ngrok

Press Ctrl+C in the ngrok terminal.