"Something went wrong setting up your Micropub endpoint" when adding an external IndieAuth/Micropub site

[svandragt]

App Version: 3.6.6 (build 434)

What happens

I'm trying to add my own self-hosted Micropub blog as a posting target in the Micro.blog iOS app, and it fails with the modal: "Sorry, something went wrong setting up your Micropub endpoint. Please try again."

The IndieAuth sign-in itself looks fine – the login and the GitHub confirmation both go through, and there's a redirect chain back into the app – but setup then falls over before my Micropub endpoint is ever contacted. The same site connects fine from other Micropub clients, so the endpoints themselves are working.

There's a long-running thread on the help forum describing the same thing, where it was put down to an app-side regression: https://help.micro.blog/t/debugging-micropub-setup/1995 ("This used to work but
something broke when we rewrote the app.")

How to reproduce

1. Have a self-hosted site that advertises authorization_endpoint, token_endpoint and micropub rel links and
   passes micropub.rocks. Mine uses authorization_endpoint = https://indieauth.com/auth and token_endpoint =
   https://tokens.indieauth.com/token.
2. Add the site as a Micropub posting target in the iOS app.
3. Complete the IndieAuth login via GitHub and approve.
4. The error modal appears after the redirect chain.

What I expected

The app completes the token exchange, gets an access token, queries the Micropub endpoint with q=config, and registers the site.

What actually happens

It fails at the auth step. I added request logging to my Micropub server, and during a failed setup nothing from the iOS app ever reaches the Micropub endpoint – the only Micropub traffic I see is from other clients. So whatever goes wrong, it goes wrong during the IndieAuth token exchange, before Micropub is involved at all.

The code I think is involved

The auth-code capture and the token-exchange request are here:

microblog-react/src/api/MicroPubApi.js

Lines 114 to 123 in d21d0a5

	async verify_code(service, auth_url) {
	const regex = /[?&]code=([^&]+)/
	const match = regex.exec(auth_url)
	if (match) {
	const auth_code = match[1];
	console.log("Micropub: Got code:", auth_code);
	console.log("Micropub: Sending to", service.token_endpoint)
	var params_s = ""
	params_s = params_s + "client_id=" + encodeURIComponent("https://micro.blog/")
	params_s = params_s + "&code=" + encodeURIComponent(auth_code)

Someone on the forum thread above reckons the encoding of the auth code in that request is the trigger – they said that dropping the encodeURIComponent and sending the auth_code raw makes verification succeed. I haven't verified that myself, so I'm not claiming it as the cause; I'm just pointing at the code path that lines up with what I'm seeing.

Environment

• Micro.blog for iOS, version 3.66 (build 434)
• iOS 26.5.
• Other Micropub iOS clients (iA Writer) connect to the same site without trouble, and the site passes
  micropub.rocks.
• Auth/token endpoints: indieauth.com / tokens.indieauth.com.

Anything else

Reported by a few people on the forum since at least September 2024, and the macOS client apparently works, so this seems to be iOS only.