DigestAuth - HTTP Digest authentication (password never on the wire)

Layer: L6 Presentation · Build flags: PC_ENABLE_AUTH (on by default)

What this example teaches

This is BasicAuth with one change: pass digest=true to the authenticated on() overload and the route is protected with HTTP Digest (RFC 7616, SHA-256, qop="auth") instead of Basic. With Digest the password never crosses the wire - only a salted hash of it does - and unauthenticated requests get a 401 plus a WWW-Authenticate: Digest challenge automatically.

One extra argument. The signature is the same as Basic auth, with a trailing true:

// on(path, method, handler, realm, user, pass, digest=true)
server.on("/secret", HttpMethod::HTTP_GET, handle_secret, "demo", "admin", "s3cret", true);

The handler is reached only after the client computes a correct digest response from the server's nonce - so the server never sees, stores, or transmits the password in the clear.

‍Testing caveat (Windows curl). curl --digest on Windows routes Digest through SSPI/SChannel, which rejects this SHA-256 / qop="auth" challenge (SEC_E_QOP_NOT_SUPPORTED) and never sends credentials. That is a Windows-curl limitation, not a server bug - the challenge is standard RFC 7616 and works with a browser, wget, or Linux/macOS curl.

Build and run

pio ci --board=esp32dev --project-option="framework=arduino" \
  --lib="." examples/L6-Presentation/DigestAuth/DigestAuth.ino

curl --digest -u admin:s3cret http://<ip>/secret   # Linux/macOS curl, wget, or a browser

Annotated source

The complete sketch (DigestAuth.ino), reproduced verbatim with added explanatory comments:

// Copyright (C) 2026 Douglas Quigg (dstroy0) <dquigg123@gmail.com>
// SPDX-License-Identifier: AGPL-3.0-or-later
 
#include "protocore.h"
#include "network_drivers/physical/physical.h"
 
static const char *SSID = "YOUR_SSID";
static const char *PASSWORD = "YOUR_PASSWORD";
 
PC server;
 
// GET /secret - only reached after successful Digest authentication.
void handle_secret(uint8_t slot_id, HttpReq *req)
{
    (void)req;
    server.send(slot_id, 200, "text/plain", "authenticated: top secret payload");
}
 
void setup()
{
    Serial.begin(115200);
 
    init_wifi_physical(SSID, PASSWORD);
    Serial.print("Connecting to WiFi");
    while (!wifi_ready())
    {
        delay(250);
        Serial.print('.');
    }
    uint32_t ip = pc_net_egress_ip(); // library egress IP (network byte order), no Arduino WiFi
    Serial.printf("IP: %u.%u.%u.%u\n", (unsigned)(ip & 0xFF), (unsigned)((ip >> 8) & 0xFF),
                  (unsigned)((ip >> 16) & 0xFF), (unsigned)((ip >> 24) & 0xFF));
 
 
    // The trailing `true` selects Digest instead of Basic for this route.
    // on(path, method, handler, realm, user, pass, digest=true)
    server.on("/secret", HttpMethod::HTTP_GET, handle_secret, "demo", "admin", "s3cret", true);
 
    int32_t result = server.begin(80);
    if (result < 0)
    {
        Serial.printf("begin() failed (error %d)\n", result);
        return;
    }
    Serial.println("Server started on port 80");
}
 
void loop()
{
    server.handle();
}