Google OAuth 2 error redirect_uri_mismatch when using local DNS remapping

Question

When I test my ASP.Net app locally, I use a DNS tool called DNSSpeeder which takes over the DNS process for my machine. In effect, I can setup www.mysite.com locally and enter an IP address like 192.168.178.200 and in my browser just enter www.mysite.com and it launches from my local IIS web server. When I'm ready for production, I just disable DNSSpeeder so that an Internet's DNS is used to lookup my site.

The problem I am facing is when I use Google OAuth to exchange my code for a token. It returns with an error of redirect_uri_mismatch. It isn't clear to me what is actually going out on the wire to Google's server and what URI Google is seeing. The URI redirect does match what is in the API console, although that doesn't say anything about what is actually sent to Google's server after it leaves DNSSpeeder. I tried Wireshark but it shows nothing. Probably encrypted with https. Instead of using http://localhost:8080, I tried http://localhost:80 as well as http://192.168.178.200 for the Javascript origins but that didn't help.

Is it possible to use an IP address other than localhost when testing locally to get a successful token?

Answer 1

"Is it possible to use an IP address other than localhost when testing locally to get a successful token?"

Yes it is possible. My setup is that I have configured two redirect URLs in the Cloud Console, (http://www.mydomain.com/redirect and http://dev.mydomain.com/redirect).

I then edit /etc/hosts (on linux, the Windose equivalent is under system32\drivers somewhere) to map dev.mydomain.com to 127.0.0.1.

And it works just fine. You may need to tweak your app so the redirect URL is not hardcoded, but is in fact varied based on whether your app senses it's in dev or production.

One thing to be aware of is that the confiured redirect URL must be a character for character match to the actual URL. So be careful that you have both http and https variants, and also watch for a trailing slash. If necessary configure both with and without the trailing slash.