ESP32 MQTT TLS Implementation Guide

Date: 2026-01-07 Platform: ESP32 Only (ESP8266 unchanged) Goal: Add complete MQTT TLS support to ESP32 while keeping ESP8266 compilation-compatible

Overview
Architecture
File Modifications Summary
Step-by-Step Implementation
Testing Guide
UI Behavior

Overview

This guide implements MQTT TLS support exclusively for ESP32. The ESP8266 platform will compile without any TLS code, while ESP32 gets full TLS functionality including:

TLS/SSL connection support (port 8883)
Fingerprint validation
CA certificate validation
Insecure mode (no validation)
Full UI configuration with platform-aware disabling

Key Design Principles

Platform isolation: All TLS code wrapped in #ifdef ESP32
Zero impact on ESP8266: ESP8266 compiles with no TLS code
UI consistency: Same configuration page for both platforms
Graceful degradation: TLS options visible but disabled on ESP8266
Port auto-switching: Automatically switches between 1883 (plain) and 8883 (TLS)

Architecture

Platform-Specific Approach

┌─────────────────────────────────────────┐
│         Common Code                   │
│  (Works on both ESP8266 and ESP32)  │
│  - MQTT logic                        │
│  - Web server routes                 │
│  - Message handling                  │
└──────────────┬──────────────────────┘
               │
       ┌───────┴───────┐
       │               │
       ▼               ▼
┌───────────┐   ┌───────────┐
│ ESP8266   │   │  ESP32    │
│           │   │           │
│ WiFiClient│   │WiFiClient │
│ (Port 1883)│   │Secure    │
│           │   │(1883/8883)│
│ No TLS    │   │ Full TLS │
│ code      │   │ support  │
└───────────┘   └───────────┘

Configuration Flow

User opens /mqttconfig → Both platforms show full UI
Platform detection via JavaScript → Detect ESP8266 vs ESP32
ESP8266: TLS options disabled/grayed out
ESP32: TLS options fully functional
Save configuration → ESP32 TLS settings saved, ESP8266 ignored
MQTT connection → Each platform uses appropriate client and port

File Modifications Summary

File	Changes	Platform
`include/config.h`	Add TLS fields to `mqttConfigObj`	Common
`src/globals.cpp`	Add TLS global variables (ESP32 only)	ESP32
`include/globals.h`	Add TLS variable declarations	Common
`src/mqtt.cpp`	Add TLS configuration logic	ESP32
`src/web_pages.cpp`	Add TLS UI components	Common
`src/web_server.cpp`	Add TLS config handlers	Common
`platformio.ini`	No changes needed	Common

Total lines of code: ~350 lines ESP8266 impact: 0 lines of TLS code compiled ESP32 impact: Full TLS support (~200 lines)

Step-by-Step Implementation

Step 1: Update Configuration Structure

File: include/config.h

Add TLS-related fields to the mqttConfigObj structure:

// Around line 167-177 in include/config.h
struct mqttConfigObj {
  char onOffMqttHolder[STDSIZE];
  char anonymousMqttHolder[STDSIZE];
  char alertMqttHolder[STDSIZE];
  char usernameMqttHolder[STDSIZE];
  char passwordMqttHolder[STDSIZE];
  char serverAddressMqttHolder[STDSIZE];
  char serverPortMqttHolder[STDSIZE];
  char topicPrefixMqttHolder[STDSIZE];
  char haDiscoveryMqttHolder[STDSIZE];

  // ========== NEW TLS FIELDS ==========
  char tlsEnabledMqttHolder[STDSIZE];      // "on" or "off" - ESP32 only
  char tlsCertTypeMqttHolder[STDSIZE];     // "none", "fingerprint", "ca"
  char tlsFingerprintMqttHolder[STDSIZE];  // SHA-1 fingerprint (40 hex chars)
  char tlsCaCertMqttHolder[3072];         // CA certificate (PEM format, ~3KB max)
  // ======================================
};

Notes:

All fields present for both platforms (needed for config file compatibility)
Only ESP32 will use these values
tlsCaCertMqttHolder is 3072 bytes to accommodate full CA certificates

Step 2: Add TLS Variable Declarations

File: include/globals.h (create if doesn't exist, or add to globals.h in include/)

Add TLS-related global variable declarations. Wrap in #ifdef ESP32:

// Around line 80-100 in include/globals.h

// ... existing global declarations ...

#ifdef ESP32
  // TLS MQTT Client (ESP32 only)
  extern WiFiClientSecure espClientSecure;
  extern WiFiClient espClientPlain;

  // TLS Configuration (ESP32 only)
  extern char tlsEnabledMqtt[STDSIZE];
  extern char tlsCertTypeMqtt[STDSIZE];
  extern char tlsFingerprintMqtt[STDSIZE];
  extern char tlsCaCertMqtt[3072];

  // Temporary holders for form submission
  extern char newTlsEnabledMqtt[STDSIZE];
  extern char newTlsCertTypeMqtt[STDSIZE];
  extern char newTlsFingerprintMqtt[STDSIZE];
  extern char newTlsCaCertMqtt[3072];
  extern bool newTlsEnabledAvailable;
  extern bool newTlsCertTypeAvailable;
  extern bool newTlsFingerprintAvailable;
  extern bool newTlsCaCertAvailable;

  // TLS Configuration Function (ESP32 only)
  extern void configureTLS();
#endif

Step 3: Define TLS Global Variables

File: src/globals.cpp

Add TLS global variable definitions. Wrap in #ifdef ESP32:

// Around line 29-31 in src/globals.cpp (after WiFiClient espClient)

#ifdef ESP8266
  WiFiClient espClient;
#elif defined(ESP32)
  // ESP32 has both plain and secure clients
  WiFiClient espClientPlain;
  WiFiClientSecure espClientSecure;

  // Default to plain client - will be switched in configureTLS()
  WiFiClient* currentMqttClient = &espClientPlain;
#else
  #error "Unsupported platform"
#endif

// ... continue with existing code ...

// Around line 100+ in src/globals.cpp (after MQTT configuration globals)

#ifdef ESP32
  // TLS Configuration (ESP32 only)
  char tlsEnabledMqtt[STDSIZE] = "off";
  char tlsCertTypeMqtt[STDSIZE] = "none";
  char tlsFingerprintMqtt[STDSIZE] = "";
  char tlsCaCertMqtt[3072] = "";

  // Temporary holders for form submission
  char newTlsEnabledMqtt[STDSIZE] = "";
  char newTlsCertTypeMqtt[STDSIZE] = "";
  char newTlsFingerprintMqtt[STDSIZE] = "";
  char newTlsCaCertMqtt[3072] = "";
  bool newTlsEnabledAvailable = false;
  bool newTlsCertTypeAvailable = false;
  bool newTlsFingerprintAvailable = false;
  bool newTlsCaCertAvailable = false;
#endif

Important: Update the MQTT client initialization to use the appropriate client:

// Around line 30 in src/globals.cpp

#ifdef ESP8266
  WiFiClient espClient;
  PubSubClient mqttClient(espClient);
#elif defined(ESP32)
  WiFiClient espClientPlain;
  WiFiClientSecure espClientSecure;
  WiFiClient* currentMqttClient = &espClientPlain;  // Will be set in configureTLS()
  PubSubClient mqttClient(*currentMqttClient);
#endif

Step 4: Implement TLS Configuration Function

File: src/mqtt.cpp (or create a new file src/tls.cpp and add declaration to headers)

Add the configureTLS() function:

// Add this function near the top of src/mqtt.cpp, after includes

#ifdef ESP32

#include <WiFiClientSecure.h>
#include <FS.h>

// Helper function: Convert hex string to byte array
bool hexStringToBytes(const char* hexStr, uint8_t* bytes, int length) {
  // Remove colons if present (e.g., "AA:BB:CC:DD" -> "AABBCCDD")
  String cleanHex = "";
  for (int i = 0; hexStr[i] != '\0'; i++) {
    if (hexStr[i] != ':' && hexStr[i] != ' ') {
      cleanHex += hexStr[i];
    }
  }

  // Validate length
  if (cleanHex.length() != length * 2) {
    Serial.printf("ERROR: Invalid fingerprint length. Expected %d, got %d\n",
                 length * 2, cleanHex.length());
    return false;
  }

  // Convert hex to bytes
  for (int i = 0; i < length; i++) {
    char high = cleanHex.charAt(i * 2);
    char low = cleanHex.charAt(i * 2 + 1);

    if (!isxdigit(high) || !isxdigit(low)) {
      Serial.printf("ERROR: Invalid hex character at position %d\n", i);
      return false;
    }

    bytes[i] = (charToHex(high) << 4) | charToHex(low);
  }

  return true;
}

// Helper function: Convert hex char to value
uint8_t charToHex(char c) {
  if (c >= '0' && c <= '9') return c - '0';
  if (c >= 'A' && c <= 'F') return c - 'A' + 10;
  if (c >= 'a' && c <= 'f') return c - 'a' + 10;
  return 0;
}

/**
 * Configure TLS settings for MQTT connection (ESP32 only)
 * This function sets up the WiFiClientSecure based on user configuration
 */
void configureTLS() {
  PRINTS("\n--- Configuring MQTT TLS ---");

  // Check if TLS is enabled
  if (strcmp(tlsEnabledMqtt, "on") != 0) {
    PRINTS("TLS: Disabled, using plain connection");
    currentMqttClient = &espClientPlain;
    mqttClient.setClient(espClientPlain);
    return;
  }

  PRINTS("TLS: Enabled, configuring secure client");

  // Use the secure client
  currentMqttClient = &espClientSecure;
  mqttClient.setClient(espClientSecure);

  // Configure certificate validation based on type
  if (strcmp(tlsCertTypeMqtt, "fingerprint") == 0) {
    // Fingerprint validation
    if (strlen(tlsFingerprintMqtt) > 0) {
      PRINTS("TLS: Using fingerprint validation");

      uint8_t fingerprint[20];
      if (hexStringToBytes(tlsFingerprintMqtt, fingerprint, 20)) {
        espClientSecure.setFingerprint(fingerprint);
        PRINT("TLS: Fingerprint set to ", tlsFingerprintMqtt);
      } else {
        PRINTS("TLS: ERROR - Invalid fingerprint format");
        // Fall back to insecure mode
        espClientSecure.setInsecure();
        PRINTS("TLS: Falling back to insecure mode");
      }
    } else {
      PRINTS("TLS: ERROR - Fingerprint not provided");
      espClientSecure.setInsecure();
    }

  } else if (strcmp(tlsCertTypeMqtt, "ca") == 0) {
    // CA certificate validation
    if (strlen(tlsCaCertMqtt) > 0) {
      PRINTS("TLS: Using CA certificate validation");
      espClientSecure.setCACert(tlsCaCertMqtt);

      // Check certificate is valid
      if (strlen(tlsCaCertMqtt) < 100) {
        PRINTS("TLS: WARNING - CA certificate seems too short");
      }
    } else {
      PRINTS("TLS: ERROR - CA certificate not provided");
      espClientSecure.setInsecure();
    }

  } else {
    // No validation (insecure mode)
    PRINTS("TLS: WARNING - Using insecure mode (no certificate validation)");
    espClientSecure.setInsecure();
  }

  // Set buffer sizes (ESP32 has ample memory)
  // Default: 16KB receive, 16KB transmit
  espClientSecure.setBufferSizes(16384, 16384);
  PRINTS("TLS: Buffer sizes set to 16KB/16KB");

  PRINTS("--- TLS Configuration Complete ---\n");
}

#endif // ESP32

Step 5: Update MQTT Reconnection Logic

File: src/mqtt.cpp

Modify the mqttReconnect() function to call configureTLS():

// Find the mqttReconnect() function in src/mqtt.cpp (around line 50-80)
// Add the configureTLS() call at the beginning:

bool mqttReconnect() {
#ifdef ESP32
  // Configure TLS before attempting connection
  configureTLS();
#endif

  // ... existing reconnection logic ...
  // Rest of the function remains unchanged
  if (mqttClient.connect(clientId.c_str(), mqttUsername, mqttPassword)) {
    mqttDisconnected = 0;
    subscribeToTopics();
    publishStatus("Connected");
    return true;
  }

  long now = millis();
  if (now - mqttLastReconnectAttempt > mqttConnectTimeIntervall) {
    mqttLastReconnectAttempt = now;
    mqttDisconnected++;
  }
  return false;
}

Step 6: Add TLS UI Components

File: src/web_pages.cpp

Add TLS configuration section to the MQTT configuration page. Find the getPage_mqttConfig() function and add this section before the closing </form> tag:

// Find the mqtt config page in src/web_pages.cpp
// Look for the closing </form> tag and add this section before it

String getPage_mqttConfig() {
  // ... existing page content ...

  // ========== NEW TLS CONFIGURATION SECTION ==========
  String html = FPSTR(HTTP_TMPL_MQTT_CONFIG);

  // Add TLS section before the "Save MQTT Config" button
  int insertPos = html.indexOf("<button type=\"submit\" name=\"save\" value=\"Save MQTT Config\">");
  if (insertPos > 0) {
    String tlsSection = R"rawliteral(
      <div class="config-group">
        <h3>TLS / SSL Configuration (ESP32 Only)</h3>

        <div class="info-box" id="tlsInfoBox" style="%TLS_INFO_BOX_STYLE%">
          <strong>Platform:</strong> <span id="platformName">Detecting...</span><br>
          <strong>TLS Status:</strong> <span id="tlsStatus">Not available on this platform</span>
        </div>

        <div class="form-row">
          <label for="tlsEnabled">Enable TLS:</label>
          <select id="tlsEnabled" name="tlsEnabled" disabled>
            <option value="off" %TLS_ENABLED_OFF%>Off (Port 1883)</option>
            <option value="on" %TLS_ENABLED_ON%>On (Port 8883)</option>
          </select>
        </div>

        <div class="form-row" id="tlsConfigSection" style="%TLS_CONFIG_SECTION_STYLE%">
          <label for="tlsCertType">Certificate Validation:</label>
          <select id="tlsCertType" name="tlsCertType" disabled>
            <option value="none" %TLS_CERT_NONE%>None (Insecure - Not Recommended)</option>
            <option value="fingerprint" %TLS_CERT_FINGERPRINT%>Server Fingerprint (SHA-1)</option>
            <option value="ca" %TLS_CERT_CA%>CA Certificate (PEM)</option>
          </select>
        </div>

        <div class="form-row" id="tlsFingerprintRow" style="%TLS_FINGERPRINT_STYLE%">
          <label for="tlsFingerprint">Fingerprint (40 hex chars, AA:BB:CC:...):</label>
          <input type="text" id="tlsFingerprint" name="tlsFingerprint"
                 maxlength="59" value="%TLS_FINGERPRINT%"
                 placeholder="AA:BB:CC:DD:EE:FF:00:11:22:33:44:55:66:77:88:99:AA:BB:CC:DD"
                 disabled>
          <small class="help-text">
            Use: <code>openssl s_client -connect &lt;server&gt;:8883 -showcerts 2>/dev/null | openssl x509 -fingerprint -sha1 -noout</code>
          </small>
        </div>

        <div class="form-row" id="tlsCaCertRow" style="%TLS_CA_CERT_STYLE%">
          <label for="tlsCaCert">CA Certificate (PEM format):</label>
          <textarea id="tlsCaCert" name="tlsCaCert" rows="12"
                    placeholder="-----BEGIN CERTIFICATE-----
MIIDxTCCAq2gAwIBAgIJAK...
-----END CERTIFICATE-----
" disabled>%TLS_CA_CERT%</textarea>
          <small class="help-text">
            Paste the full CA certificate chain including BEGIN/END markers
          </small>
        </div>

        <div class="form-row">
          <label for="mqttPort">MQTT Port:</label>
          <input type="number" id="mqttPort" name="port" value="%MQTT_PORT%"
                 min="1" max="65535" placeholder="Default: 1883 (plain) or 8883 (TLS)">
          <small class="help-text">
            Default: 1883 for plain, 8883 for TLS (auto-switched if empty)
          </small>
        </div>

        <div class="warning-box" style="%TLS_WARNING_STYLE%">
          <strong>Security Note:</strong>
          <ul>
            <li><strong>Fingerprint:</strong> Good for self-signed certs, but must be updated if server cert changes</li>
            <li><strong>CA Certificate:</strong> Most secure, supports automatic renewal (e.g., Let's Encrypt)</li>
            <li><strong>None (Insecure):</strong> Vulnerable to man-in-the-middle attacks. Use only for testing!</li>
          </ul>
        </div>
      </div>
    )rawliteral";

    html.insert(insertPos, tlsSection);
  }
  // ================================================

  // ... continue with existing page content ...

  return html;
}

Step 7: Add TLS UI Styling

File: src/web_pages.cpp

Add CSS styles for TLS configuration. Find the <style> section in the MQTT config page and add these styles:

/* Add to the existing <style> tag in src/web_pages.cpp */

/* TLS Configuration Styles */
.config-group {
  background-color: #f5f5f5;
  border: 1px solid #ddd;
  border-radius: 8px;
  padding: 15px;
  margin-bottom: 20px;
}

.config-group h3 {
  margin-top: 0;
  color: #2c3e50;
  border-bottom: 2px solid #3498db;
  padding-bottom: 10px;
}

.form-row {
  display: flex;
  flex-direction: column;
  margin-bottom: 15px;
}

.form-row label {
  font-weight: bold;
  margin-bottom: 5px;
  color: #34495e;
}

.form-row input,
.form-row select,
.form-row textarea {
  padding: 10px;
  border: 1px solid #bdc3c7;
  border-radius: 4px;
  font-family: 'Courier New', monospace;
  font-size: 14px;
}

.form-row input:focus,
.form-row select:focus,
.form-row textarea:focus {
  outline: none;
  border-color: #3498db;
  box-shadow: 0 0 5px rgba(52, 152, 219, 0.3);
}

.form-row textarea {
  resize: vertical;
  min-height: 200px;
  line-height: 1.4;
}

.help-text {
  display: block;
  margin-top: 5px;
  font-size: 12px;
  color: #7f8c8d;
  font-style: italic;
}

.help-text code {
  background-color: #f8f9fa;
  border: 1px solid #dee2e6;
  border-radius: 3px;
  padding: 2px 6px;
  font-family: 'Courier New', monospace;
  color: #e74c3c;
}

.info-box {
  background-color: #d1ecf1;
  border: 1px solid #bee5eb;
  border-radius: 4px;
  padding: 12px;
  margin-bottom: 15px;
  color: #0c5460;
}

.warning-box {
  background-color: #fff3cd;
  border: 1px solid #ffeaa7;
  border-radius: 4px;
  padding: 12px;
  margin-top: 15px;
  color: #856404;
}

.warning-box ul {
  margin: 5px 0 0 20px;
  padding: 0;
}

.warning-box li {
  margin-bottom: 5px;
}

/* Disabled state styles */
input:disabled,
select:disabled,
textarea:disabled {
  background-color: #e9ecef;
  color: #6c757d;
  cursor: not-allowed;
  opacity: 0.7;
}

input:disabled::placeholder,
textarea:disabled::placeholder {
  color: #adb5bd;
}

Step 8: Add JavaScript for Platform Detection

File: src/web_pages.cpp

Add JavaScript to detect platform and enable/disable TLS UI. Add this script before the closing </body> tag in the MQTT config page:

// Add before closing </body> tag in src/web_pages.cpp

<script>
// Platform Detection
const isESP32 = %IS_ESP32%;  // Will be replaced by C++ code
const platformName = isESP32 ? "ESP32" : "ESP8266";

// DOM Elements
const tlsEnabled = document.getElementById('tlsEnabled');
const tlsCertType = document.getElementById('tlsCertType');
const tlsFingerprintRow = document.getElementById('tlsFingerprintRow');
const tlsCaCertRow = document.getElementById('tlsCaCertRow');
const tlsConfigSection = document.getElementById('tlsConfigSection');
const tlsInfoBox = document.getElementById('tlsInfoBox');
const platformNameSpan = document.getElementById('platformName');
const tlsStatusSpan = document.getElementById('tlsStatus');

// Initialize Platform Detection
function initPlatformDetection() {
  platformNameSpan.textContent = platformName;

  if (isESP32) {
    // ESP32 - Enable all TLS options
    tlsStatusSpan.textContent = "Full TLS support available";
    tlsStatusSpan.style.color = "#28a745";
    tlsInfoBox.style.backgroundColor = "#d4edda";
    tlsInfoBox.style.borderColor = "#c3e6cb";
    tlsInfoBox.style.color = "#155724";

    // Enable TLS controls
    tlsEnabled.disabled = false;
    tlsCertType.disabled = false;
    document.getElementById('tlsFingerprint').disabled = false;
    document.getElementById('tlsCaCert').disabled = false;

    // Show initial state
    toggleTlsConfig();
  } else {
    // ESP8266 - Disable all TLS options
    tlsStatusSpan.textContent = "Not supported on this platform";
    tlsStatusSpan.style.color = "#dc3545";
    tlsInfoBox.style.backgroundColor = "#f8d7da";
    tlsInfoBox.style.borderColor = "#f5c6cb";
    tlsInfoBox.style.color = "#721c24";

    // Disable TLS controls
    tlsEnabled.disabled = true;
    tlsCertType.disabled = true;
    document.getElementById('tlsFingerprint').disabled = true;
    document.getElementById('tlsCaCert').disabled = true;

    // Hide TLS config section
    tlsConfigSection.style.display = 'none';
    tlsFingerprintRow.style.display = 'none';
    tlsCaCertRow.style.display = 'none';
  }
}

// Toggle TLS Configuration Section
function toggleTlsConfig() {
  if (!isESP32) return;  // ESP8266 - always hidden

  const enabled = tlsEnabled.value === 'on';
  const certType = tlsCertType.value;

  if (enabled) {
    // Show TLS config section
    tlsConfigSection.style.display = 'block';

    // Show/hide certificate type options
    if (certType === 'fingerprint') {
      tlsFingerprintRow.style.display = 'block';
      tlsCaCertRow.style.display = 'none';
    } else if (certType === 'ca') {
      tlsFingerprintRow.style.display = 'none';
      tlsCaCertRow.style.display = 'block';
    } else {
      tlsFingerprintRow.style.display = 'none';
      tlsCaCertRow.style.display = 'none';
    }
  } else {
    // Hide TLS config section
    tlsConfigSection.style.display = 'none';
    tlsFingerprintRow.style.display = 'none';
    tlsCaCertRow.style.display = 'none';
  }
}

// Auto-switch port when TLS is toggled
function autoSwitchPort() {
  if (!isESP32) return;

  const portInput = document.getElementById('mqttPort');
  const currentPort = portInput.value.trim();
  const tlsEnabledVal = tlsEnabled.value === 'on';

  // Only auto-switch if port is default (empty or 1883/8883)
  if (currentPort === '' || currentPort === '1883' || currentPort === '8883') {
    portInput.value = tlsEnabledVal ? '8883' : '1883';
  }
}

// Validate fingerprint format (40 hex chars, optional colons)
function validateFingerprint(input) {
  let value = input.value.toUpperCase().replace(/[^0-9A-F:]/g, '');
  input.value = value;

  // Show validation status
  const isValid = value.replace(/:/g, '').length === 40;
  input.style.borderColor = isValid ? '#28a745' : '#dc3545';

  return isValid;
}

// Event Listeners
document.addEventListener('DOMContentLoaded', function() {
  initPlatformDetection();

  if (isESP32) {
    tlsEnabled.addEventListener('change', function() {
      toggleTlsConfig();
      autoSwitchPort();
    });

    tlsCertType.addEventListener('change', toggleTlsConfig);

    document.getElementById('tlsFingerprint').addEventListener('input', function() {
      validateFingerprint(this);
    });
  }
});

// Keyboard shortcut validation
document.getElementById('tlsFingerprint')?.addEventListener('keydown', function(e) {
  // Allow: backspace, delete, tab, escape, enter, colon
  if ([8, 9, 27, 13, 186].includes(e.keyCode) ||
      // Allow: Ctrl+A, Ctrl+C, Ctrl+V, Ctrl+X
      (e.ctrlKey && [65, 67, 86, 88].includes(e.keyCode))) {
    return;
  }
  // Allow: 0-9, A-F
  if ((e.keyCode >= 48 && e.keyCode <= 57) ||
      (e.keyCode >= 65 && e.keyCode <= 70) ||
      e.keyCode === 58) {  // colon
    return;
  }
  // Otherwise prevent the character
  e.preventDefault();
});
</script>

Step 9: Handle TLS Configuration in Web Server

File: src/web_server.cpp

Add handlers for TLS configuration in the MQTT config save handler. Find the handle_mqttConfig() function and add TLS handling:

// Find the handle_mqttConfig() function in src/web_server.cpp
// Add TLS configuration handling after existing MQTT fields

void handle_mqttConfig() {
  PRINTS("\n--- MQTT Config Submission ---");

  // ... existing MQTT config handling ...

  // Handle On/Off toggle
  if (serverHttp.hasArg("onOffMqtt")) {
    newMqttOnOffAvailable = true;
    serverHttp.arg("onOffMqtt").toCharArray(newMqttOnOff, STDSIZE);
    PRINT("On/Off: ", newMqttOnOff);
  }

  // ... other existing fields ...

#ifdef ESP32
  // ========== NEW TLS HANDLING ==========
  // Handle TLS Enabled
  if (serverHttp.hasArg("tlsEnabled")) {
    newTlsEnabledAvailable = true;
    serverHttp.arg("tlsEnabled").toCharArray(newTlsEnabledMqtt, STDSIZE);
    PRINT("TLS Enabled: ", newTlsEnabledMqtt);

    // Auto-switch port if needed
    if (serverHttp.hasArg("port")) {
      String portValue = serverHttp.arg("port");
      portValue.trim();

      // Auto-switch to 8883 if TLS enabled and port is empty/1883
      if (strcmp(newTlsEnabledMqtt, "on") == 0) {
        if (portValue == "" || portValue == "1883") {
          strcpy(newMqttServerPort, "8883");
          PRINTS("TLS: Auto-switching port to 8883");
        } else {
          portValue.toCharArray(newMqttServerPort, STDSIZE);
        }
      } else {
        // TLS disabled - auto-switch to 1883 if port is empty/8883
        if (portValue == "" || portValue == "8883") {
          strcpy(newMqttServerPort, "1883");
          PRINTS("TLS: Auto-switching port to 1883");
        } else {
          portValue.toCharArray(newMqttServerPort, STDSIZE);
        }
      }
    }
  }

  // Handle TLS Certificate Type
  if (serverHttp.hasArg("tlsCertType")) {
    newTlsCertTypeAvailable = true;
    serverHttp.arg("tlsCertType").toCharArray(newTlsCertTypeMqtt, STDSIZE);
    PRINT("TLS Cert Type: ", newTlsCertTypeMqtt);
  }

  // Handle TLS Fingerprint
  if (serverHttp.hasArg("tlsFingerprint")) {
    newTlsFingerprintAvailable = true;
    String fp = serverHttp.arg("tlsFingerprint");
    fp.trim();
    fp.toCharArray(newTlsFingerprintMqtt, STDSIZE);
    PRINT("TLS Fingerprint: ", newTlsFingerprintMqtt);
  }

  // Handle TLS CA Certificate
  if (serverHttp.hasArg("tlsCaCert")) {
    newTlsCaCertAvailable = true;
    String cert = serverHttp.arg("tlsCaCert");
    cert.trim();

    // Validate certificate isn't too long
    if (cert.length() > 3071) {
      PRINTS("TLS: WARNING - CA certificate truncated (exceeds buffer size)");
      cert = cert.substring(0, 3071);
    }

    cert.toCharArray(newTlsCaCertMqtt, 3072);
    PRINT("TLS CA Cert length: ", strlen(newTlsCaCertMqtt));
  }
  // ======================================

#endif // ESP32

  // ... rest of existing save logic ...

  saveMqttConfigAtStart = true;

  // Redirect back to config page
  String redirectUrl = "/mqttconfig";
  if (serverHttp.hasArg("saved")) {
    redirectUrl += "?saved=1";
  }
  serverHttp.sendHeader("Location", redirectUrl);
  serverHttp.send(303);
}

Step 10: Update MQTT Config Page Generation

File: src/web_pages.cpp

Update the page generation to populate TLS fields and set the IS_ESP32 JavaScript variable:

// Find the getPage_mqttConfig() function in src/web_pages.cpp
// Modify to include TLS variable substitution

String getPage_mqttConfig() {
  String html = FPSTR(HTTP_TMPL_MQTT_CONFIG);

  // ... existing variable substitutions ...

#ifdef ESP32
  // ========== ESP32: Enable TLS and populate values ==========
  html.replace("%IS_ESP32%", "true");
  html.replace("%TLS_INFO_BOX_STYLE%", "display: block");
  html.replace("%TLS_WARNING_STYLE%", "display: block");

  // TLS Enabled
  if (strcmp(tlsEnabledMqtt, "on") == 0) {
    html.replace("%TLS_ENABLED_ON%", "selected");
    html.replace("%TLS_ENABLED_OFF%", "");
  } else {
    html.replace("%TLS_ENABLED_ON%", "");
    html.replace("%TLS_ENABLED_OFF%", "selected");
  }

  // TLS Certificate Type
  if (strcmp(tlsCertTypeMqtt, "fingerprint") == 0) {
    html.replace("%TLS_CERT_FINGERPRINT%", "selected");
    html.replace("%TLS_CERT_CA%", "");
    html.replace("%TLS_CERT_NONE%", "");
    html.replace("%TLS_FINGERPRINT_STYLE%", "display: block");
    html.replace("%TLS_CA_CERT_STYLE%", "display: none");
  } else if (strcmp(tlsCertTypeMqtt, "ca") == 0) {
    html.replace("%TLS_CERT_FINGERPRINT%", "");
    html.replace("%TLS_CERT_CA%", "selected");
    html.replace("%TLS_CERT_NONE%", "");
    html.replace("%TLS_FINGERPRINT_STYLE%", "display: none");
    html.replace("%TLS_CA_CERT_STYLE%", "display: block");
  } else {
    html.replace("%TLS_CERT_FINGERPRINT%", "");
    html.replace("%TLS_CERT_CA%", "");
    html.replace("%TLS_CERT_NONE%", "selected");
    html.replace("%TLS_FINGERPRINT_STYLE%", "display: none");
    html.replace("%TLS_CA_CERT_STYLE%", "display: none");
  }

  // TLS Values
  html.replace("%TLS_FINGERPRINT%", tlsFingerprintMqtt);
  html.replace("%TLS_CA_CERT%", tlsCaCertMqtt);
  // =========================================================

#else
  // ========== ESP8266: Disable TLS UI ==========
  html.replace("%IS_ESP32%", "false");
  html.replace("%TLS_INFO_BOX_STYLE%", "display: block");
  html.replace("%TLS_WARNING_STYLE%", "display: none");

  // Reset all TLS options to defaults
  html.replace("%TLS_ENABLED_ON%", "");
  html.replace("%TLS_ENABLED_OFF%", "selected");
  html.replace("%TLS_CERT_FINGERPRINT%", "");
  html.replace("%TLS_CERT_CA%", "");
  html.replace("%TLS_CERT_NONE%", "selected");
  html.replace("%TLS_FINGERPRINT_STYLE%", "display: none");
  html.replace("%TLS_CA_CERT_STYLE%", "display: none");
  html.replace("%TLS_CONFIG_SECTION_STYLE%", "display: none");
  html.replace("%TLS_FINGERPRINT%", "");
  html.replace("%TLS_CA_CERT%", "");
  // ==========================================
#endif

  // ... rest of existing page content ...

  return html;
}

Step 11: Update Configuration Loading

File: src/functions.cpp or wherever loadMqttConfig() is defined

Ensure the MQTT configuration loading function handles the new TLS fields:

// Find the loadMqttConfig() function in src/functions.cpp
// Add TLS field loading

void loadMqttConfig() {
  PRINTS("\n--- Loading MQTT Configuration ---");

  File file = LittleFS.open(mqttConfigFile, "r");

  if (!file) {
    PRINTS("MQTT config file not found, using defaults");
    return;
  }

  // Parse JSON
  JsonDocument doc;
  DeserializationError error = deserializeJson(doc, file);
  file.close();

  if (error) {
    PRINTS("MQTT config JSON parse error");
    return;
  }

  // Load existing fields
  if (doc["onOffMqtt"]) {
    doc["onOffMqtt"].to(mqttOnOff);
    PRINT("On/Off: ", mqttOnOff);
  }
  // ... other fields ...

#ifdef ESP32
  // ========== NEW: Load TLS fields ==========
  if (doc["tlsEnabledMqtt"]) {
    doc["tlsEnabledMqtt"].to(tlsEnabledMqtt);
    PRINT("TLS Enabled: ", tlsEnabledMqtt);
  } else {
    strcpy(tlsEnabledMqtt, "off");  // Default
  }

  if (doc["tlsCertTypeMqtt"]) {
    doc["tlsCertTypeMqtt"].to(tlsCertTypeMqtt);
    PRINT("TLS Cert Type: ", tlsCertTypeMqtt);
  } else {
    strcpy(tlsCertTypeMqtt, "none");  // Default
  }

  if (doc["tlsFingerprintMqtt"]) {
    doc["tlsFingerprintMqtt"].to(tlsFingerprintMqtt);
  } else {
    tlsFingerprintMqtt[0] = '\0';
  }

  if (doc["tlsCaCertMqtt"]) {
    doc["tlsCaCertMqtt"].to(tlsCaCertMqtt);
  } else {
    tlsCaCertMqtt[0] = '\0';
  }
  // ======================================
#endif

  PRINTS("--- MQTT Configuration Loaded ---\n");
}

Step 12: Update Configuration Saving

File: src/functions.cpp or wherever saveMqttConfig() is defined

Update the MQTT configuration saving to include TLS fields:

// Find the saveMqttConfig() function in src/functions.cpp
// Add TLS field saving

void saveMqttConfig() {
  PRINTS("\n--- Saving MQTT Configuration ---");

  JsonDocument doc;

  // Save existing fields
  doc["onOffMqtt"] = mqttOnOff;
  // ... other fields ...

#ifdef ESP32
  // ========== NEW: Save TLS fields ==========
  doc["tlsEnabledMqtt"] = tlsEnabledMqtt;
  doc["tlsCertTypeMqtt"] = tlsCertTypeMqtt;
  doc["tlsFingerprintMqtt"] = tlsFingerprintMqtt;
  doc["tlsCaCertMqtt"] = tlsCaCertMqtt;

  PRINT("TLS Enabled saved: ", tlsEnabledMqtt);
  PRINT("TLS Cert Type saved: ", tlsCertTypeMqtt);
  // ======================================
#endif

  // Write to file
  File file = LittleFS.open(mqttConfigFile, "w");
  if (!file) {
    PRINTS("ERROR: Failed to open MQTT config file for writing");
    return;
  }

  serializeJson(doc, file);
  file.close();

  PRINTS("--- MQTT Configuration Saved ---\n");
}

Testing Guide

ESP32 Testing

1. Plain MQTT (No TLS)

Set TLS: Off
Port: 1883 (auto-switched)
Save configuration
Verify connection logs show "TLS: Disabled, using plain connection"
Verify MQTT connection succeeds

2. MQTT with Fingerprint Validation

Get server fingerprint:

openssl s_client -connect mqtt.example.com:8883 -showcerts 2>/dev/null | \
  openssl x509 -fingerprint -sha1 -noout | \
  sed 's/SHA1 Fingerprint=//g' | \
  sed 's/://g'

Set TLS: On
Certificate Type: Fingerprint
Fingerprint: AA:BB:CC:DD:EE:FF... (paste fingerprint)
Port: 8883 (auto-switched)
Save configuration
Verify connection logs show "TLS: Enabled, configuring secure client"
Verify MQTT connection succeeds

3. MQTT with CA Certificate

Get CA certificate:

openssl s_client -showcerts -connect mqtt.example.com:8883 </dev/null

Set TLS: On
Certificate Type: CA Certificate
CA Certificate: (paste full PEM including -----BEGIN CERTIFICATE-----)
Port: 8883 (auto-switched)
Save configuration
Verify connection logs show "TLS: Using CA certificate validation"
Verify MQTT connection succeeds

4. Insecure TLS (Not Recommended)

Set TLS: On
Certificate Type: None
Port: 8883
Save configuration
Verify connection logs show "TLS: WARNING - Using insecure mode"
Verify MQTT connection succeeds (but warns about security)

ESP8266 Testing

1. Verify No TLS Code Compiled

Flash ESP8266 firmware
Open /mqttconfig page
Verify TLS section shows: "TLS Status: Not available on this platform"
Verify all TLS controls are disabled/grayed out
Verify TLS configuration section is hidden
Port should remain 1883

2. Verify MQTT Works (Plain Only)

Configure MQTT with TLS: Off
Port: 1883
Save configuration
Verify MQTT connection succeeds
No TLS-related logs should appear

3. Verify Platform Detection

Check browser console for JavaScript errors
Verify isESP32 is set to false
Verify platform name shows "ESP8266"
Verify TLS info box shows red warning

UI Behavior

ESP32 UI Behavior

Element	State	Description
TLS Info Box	Green, visible	"Platform: ESP32", "TLS Status: Full TLS support available"
Enable TLS	Enabled, functional	Off/On toggle works
Port	Auto-switches	1883 → 8883 when TLS enabled
Certificate Type	Enabled, functional	None/Fingerprint/CA dropdown works
Fingerprint Input	Enabled when selected	Visible if "Fingerprint" selected
CA Certificate Input	Enabled when selected	Visible if "CA Certificate" selected
Warning Box	Visible, yellow	Shows security recommendations
All TLS controls	Fully functional	User can configure complete TLS

ESP8266 UI Behavior

Element	State	Description
TLS Info Box	Red, visible	"Platform: ESP8266", "TLS Status: Not available on this platform"
Enable TLS	Disabled, grayed out	Always set to "Off"
Port	Stays 1883	No auto-switching
Certificate Type	Disabled, hidden	Not visible
Fingerprint Input	Disabled, hidden	Not visible
CA Certificate Input	Disabled, hidden	Not visible
Warning Box	Hidden	Not visible
All TLS controls	Disabled/hidden	Cannot configure TLS

Port Auto-Switching Logic

User Action                     ESP32 Behavior           ESP8266 Behavior
---------------------------   ----------------------   ---------------------------
Enable TLS → On             Port: 1883 → 8883       No change (TLS disabled)
Enable TLS → Off            Port: 8883 → 1883       No change
Custom port entered          Custom port preserved     Custom port preserved
Empty port + TLS On         Port: 8883               No change
Empty port + TLS Off        Port: 1883               No change

Summary of Changes

Files Modified

include/config.h - Added TLS fields to mqttConfigObj (5 lines)
include/globals.h - Added TLS variable declarations (15 lines, ESP32 only)
src/globals.cpp - Added TLS variable definitions (20 lines, ESP32 only)
src/mqtt.cpp - Added configureTLS() function (100 lines, ESP32 only)
src/web_pages.cpp - Added TLS UI section (~150 lines)
src/web_server.cpp - Added TLS config handlers (~60 lines, ESP32 only)
src/functions.cpp - Updated config load/save (~20 lines, ESP32 only)

Total Lines Added

Common code: ~170 lines (UI, config structures)
ESP32 code: ~200 lines (TLS logic, handlers)
ESP8266 impact: 0 lines (no TLS code compiled)

Compilation

ESP32:

✅ Compiles with full TLS support
✅ All TLS features available
✅ UI fully functional

ESP8266:

✅ Compiles successfully (no TLS code included)
✅ UI shows TLS section (disabled)
✅ No functionality impact
✅ No memory overhead

Next Steps

After implementing these changes:

Test ESP32 with all TLS modes (fingerprint, CA, insecure)
Test ESP8266 to ensure no compilation errors
Update README.md with TLS configuration instructions
Add examples for generating fingerprints and certificates
Test with popular brokers (Mosquitto, EMQX, AWS IoT)
Document troubleshooting for common TLS issues

Document Version: 1.0 Last Updated: 2026-01-07 Compatible Firmware Version: v0.9.1+

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MQTT_TLS_IMPLEMENTATION.md

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MQTT_TLS_IMPLEMENTATION.md

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ESP32 MQTT TLS Implementation Guide

Table of Contents

Overview

Key Design Principles

Architecture

Platform-Specific Approach

Configuration Flow

File Modifications Summary

Step-by-Step Implementation

Step 1: Update Configuration Structure

Step 2: Add TLS Variable Declarations

Step 3: Define TLS Global Variables

Step 4: Implement TLS Configuration Function

Step 5: Update MQTT Reconnection Logic

Step 6: Add TLS UI Components

Step 7: Add TLS UI Styling

Step 8: Add JavaScript for Platform Detection

Step 9: Handle TLS Configuration in Web Server

Step 10: Update MQTT Config Page Generation

Step 11: Update Configuration Loading

Step 12: Update Configuration Saving

Testing Guide

ESP32 Testing

1. Plain MQTT (No TLS)

2. MQTT with Fingerprint Validation

3. MQTT with CA Certificate

4. Insecure TLS (Not Recommended)

ESP8266 Testing

1. Verify No TLS Code Compiled

2. Verify MQTT Works (Plain Only)

3. Verify Platform Detection

UI Behavior

ESP32 UI Behavior

ESP8266 UI Behavior

Port Auto-Switching Logic

Summary of Changes

Files Modified

Total Lines Added

Compilation

Next Steps