Anything in the server logs?

Turned debug logging on and tried again, nothing interesting I can see.

2021-07-04T13:56:32Z - Configured upstream IMAP server: <mail server>
2021-07-04T13:56:32Z - Configured upstream SMTP server: <mail server>
2021-07-04T13:56:32Z - Loaded plugin "base"
2021-07-04T13:56:32Z - Loaded plugin "viewhtml"
2021-07-04T13:56:32Z - Loaded plugin "viewtext"
2021-07-04T13:56:32Z - Loading theme "alps"
2021-07-04T13:56:32Z - Loading theme "sourcehut"
⇨ http server started on 0.0.0.0:1323
2021-07-04T13:56:35Z method=GET, uri=/login?next=%2Fmailbox%2FINBOX, status=200

Will do some more digging.

I added some logging, seems the cookie is getting lost somehow. Logging:

@@ -315,6 +315,11 @@ func (ctx *Context) SetLoginToken(username, password string) {
 func (ctx *Context) GetLoginToken() (string, string) {
        cookie, err := ctx.Cookie(loginTokenCookieName)
        if err != nil || cookie == nil {
+               if err != nil {
+                       log.Println(err)
+               } else {
+                       log.Println("cookie is null")
+               }
                return "", ""
        }

Result:

⇨ http server started on 0.0.0.0:1323
2021/07/04 14:07:47 http: named cookie not present

I thought it might be the reverse proxy, but it's much simpler than that:

The loginToken cookie is only set if the 'remember me' checkbox is ticked on the login page. This checkbox is only present in the 'alps' theme, not the base or sourcehut themes.

It should probably be added to those themes I guess.

Separately, the alps theme crashes when it tries to load my inbox, but another issue should be raised for that probably.

Closing; this works as expected and I've submitted a patch to clarify the documentation (thanks for accepting)

I'll open separate tickets for subsequent issues.