ESP8266 Captive portal with pop-up

Question

Has anyone ever succeeded in getting a captive portal to cause a pop-up for the redirected content to a specific landing page on an Arduino or ESP8266? I've tried everything under the sun and while my android will complain about a non-connected internet and other things, it never actually requests/suggests opening a browser as I've seen done on some open-wifi hotspots with sign-in pages. I'm trying to implement what will actually be a non-internet connected device that users would sign into at a remote location to show they had arrived, kind of like a geocache but using wifi sign in. I did the dnsServer glob (all names to local IP), I've done a number of url redirects. I've tried feeding the specific content (instead of the re-directs) but nothing pops up.

Relevant code:

#include <ESPAsyncWebServer.h>
#include <ESP8266WiFi.h>
#include <DNSServer.h>
#include <ESP8266mDNS.h>


IPAddress apIp ( 10, 10, 10, 10 );
AsyncWebServer asyncWebServer(80);
DNSServer dnsServer;
const char* captiveRedirect = "/index.htm";
String apSSID = "GeoCache";

dnsServer.setErrorReplyCode(DNSReplyCode::NoError);
dnsServer.start ( DNS_PORT, "*", apIp );

DBG_OUTPUT_PORT.println("Initializing MDNS for local hostname on AP");
if (MDNS.begin(apHostname)) {
    MDNS.addService("http", "tcp", 80);
    DBG_OUTPUT_PORT.println("MDNS responder started");
    DBG_OUTPUT_PORT.print("You can now connect to http://");
    DBG_OUTPUT_PORT.print(apHostname);
    DBG_OUTPUT_PORT.println(".local");
}

//Android captive portal. Maybe not needed. Might be handled by notFound handler.
asyncWebServer.addRewrite( new AsyncWebRewrite("/generate_204", captiveRedirect));
//asyncWebServer.on ( "/generate_204", returnOK );
//Microsoft captive portal. Maybe not needed. Might be handled by notFound handler.
asyncWebServer.addRewrite( new AsyncWebRewrite("/fwlink", captiveRedirect));
//asyncWebServer.on ( "/fwlink", returnOK );
//Microsoft windows 10
//asyncWebServer.on ( "/connecttest.txt", returnOK );
asyncWebServer.addRewrite( new AsyncWebRewrite("/connecttest.txt", captiveRedirect));
// apple devices
asyncWebServer.addRewrite( new AsyncWebRewrite("/hotspot-detect.html", captiveRedirect));
//asyncWebServer.on ( "/hotspot-detect.html", returnOK );
asyncWebServer.addRewrite( new AsyncWebRewrite("/library/test/success.html", captiveRedirect));
//asyncWebServer.on ( "/library/test/success.html", returnOK );
// kindle
asyncWebServer.addRewrite( new AsyncWebRewrite("/kindle-wifi/wifistub.html", captiveRedirect));
//asyncWebServer.on ( "/kindle-wifi/wifistub.html", returnOK );

asyncWebServer.on("/delete", HTTP_DELETE, handleDelete);
// upload a file to /upload
asyncWebServer.on("/upload", HTTP_POST, returnOK, handleUpload);
// Catch-All Handlers
asyncWebServer.onFileUpload(handleUpload);
//asyncWebServer.onRequestBody(onBody);

asyncWebServer.on("/signin", HTTP_GET, addLog);

asyncWebServer.onNotFound(handleNotFound);

asyncWebServer.begin();

WiFi.mode(WIFI_AP);
WiFi.softAPConfig ( apIp, apIp, IPAddress ( 255, 255, 255, 0 ) );
WiFi.softAP(apSSID);

Answer 1

In the loop(), you have to include:

dnsServer.processNextRequest();

before

server.handleClient(); //Handling of incoming requests

then, create a notfound router:

server.onNotFound([]() {
    char * msg = "HELLO<br>Default landing page<br>";
    server.send(200, "text/html", msg );
  });