src/Socialbox/Classes/RpcClient.php

@@ -2,6 +2,7 @@
 
     namespace Socialbox\Classes;
 
+    use Socialbox\Enums\Options\ClientOptions;
     use Socialbox\Enums\StandardHeaders;
     use Socialbox\Enums\Types\RequestType;
     use Socialbox\Exceptions\CryptographyException;
@@ -60,7 +61,19 @@
 
             // Set the initial properties
             $this->peerAddress = $peerAddress;
-            $this->keyPair = Cryptography::generateKeyPair();
+
+            // If the username is `host` and the domain is the same as this server's domain, we use our keypair
+            // Essentially this is a special case for the server to contact another server
+            if($this->peerAddress->isHost())
+            {
+                $this->keyPair = new KeyPair(Configuration::getInstanceConfiguration()->getPublicKey(), Configuration::getInstanceConfiguration()->getPrivateKey());
+            }
+            // Otherwise we generate a random keypair
+            else
+            {
+                $this->keyPair = Cryptography::generateKeyPair();
+            }
+
             $this->encryptionKey = Cryptography::generateEncryptionKey();
 
             // Resolve the domain and get the server's Public Key & RPC Endpoint
@@ -97,16 +110,25 @@
         {
             $ch = curl_init();
 
-            curl_setopt($ch, CURLOPT_URL, $this->rpcEndpoint);
+            // Basic session details
-            curl_setopt($ch, CURLOPT_HTTPGET, true);
+            $headers = [
-            curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
-            curl_setopt($ch, CURLOPT_HTTPHEADER, [
                 StandardHeaders::REQUEST_TYPE->value . ': ' . RequestType::INITIATE_SESSION->value,
                 StandardHeaders::CLIENT_NAME->value . ': ' . self::CLIENT_NAME,
                 StandardHeaders::CLIENT_VERSION->value . ': ' . self::CLIENT_VERSION,
-                StandardHeaders::PUBLIC_KEY->value . ': ' . $this->keyPair->getPublicKey(),
                 StandardHeaders::IDENTIFY_AS->value . ': ' . $this->peerAddress->getAddress(),
-            ]);
+            ];
+
+            // If we're not connecting as the host, we need to provide our public key
+            // Otherwise, the server will obtain the public key itself from DNS records rather than trusting the client
+            if(!$this->peerAddress->isHost())
+            {
+                $headers[] = StandardHeaders::PUBLIC_KEY->value . ': ' . $this->keyPair->getPublicKey();
+            }
+
+            curl_setopt($ch, CURLOPT_URL, $this->rpcEndpoint);
+            curl_setopt($ch, CURLOPT_HTTPGET, true);
+            curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
+            curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
 
             $response = curl_exec($ch);
 

src/Socialbox/Enums/Options/ClientOptions.php

@@ -0,0 +1,8 @@
+<?php
+
+    namespace Socialbox\Enums\Options;
+
+    enum ClientOptions
+    {
+        case EXTERNAL_CONNECTION;
+    }

src/Socialbox/Objects/PeerAddress.php

@@ -3,6 +3,7 @@
     namespace Socialbox\Objects;
 
     use InvalidArgumentException;
+    use Socialbox\Classes\Configuration;
     use Socialbox\Classes\Validator;
     use Socialbox\Enums\ReservedUsernames;
 
@@ -67,7 +68,7 @@
          */
         public function isHost(): bool
         {
-            return $this->username === ReservedUsernames::HOST->value;
+            return $this->username === ReservedUsernames::HOST->value && $this->domain === Configuration::getInstanceConfiguration()->getDomain();
         }
 
         /**

src/Socialbox/SocialClient.php

@@ -23,6 +23,7 @@
          *
          * @param string|PeerAddress $peerAddress The address of the peer to connect to.
          * @param ExportedSession|null $exportedSession Optional. The exported session to use for communication.
+         * @param array $options Optional. Additional options to pass to the client.
          * @throws CryptographyException If the public key is invalid.
          * @throws ResolutionException If the domain cannot be resolved.
          * @throws RpcException If the RPC request fails.

src/Socialbox/Socialbox.php

@@ -7,8 +7,10 @@
     use Socialbox\Classes\Configuration;
     use Socialbox\Classes\Cryptography;
     use Socialbox\Classes\Logger;
+    use Socialbox\Classes\ServerResolver;
     use Socialbox\Classes\Utilities;
     use Socialbox\Classes\Validator;
+    use Socialbox\Enums\ReservedUsernames;
     use Socialbox\Enums\SessionState;
     use Socialbox\Enums\StandardError;
     use Socialbox\Enums\StandardHeaders;
@@ -68,6 +70,58 @@
             }
         }
 
+        /**
+         * Validates the headers in an initialization request to ensure that all
+         * required information is present and properly formatted. This includes
+         * checking for headers such as Client Name, Client Version, Public Key,
+         * and Identify-As, as well as validating the Identify-As header value.
+         * If any validation fails, a corresponding HTTP response code and message
+         * are returned.
+         *
+         * @param ClientRequest $clientRequest The client request containing headers to validate.
+         *
+         * @return bool Returns true if all required headers are valid, otherwise false.
+         */
+        private static function validateInitHeaders(ClientRequest $clientRequest): bool
+        {
+            if(!$clientRequest->getClientName())
+            {
+                http_response_code(400);
+                print('Missing required header: ' . StandardHeaders::CLIENT_NAME->value);
+                return false;
+            }
+
+            if(!$clientRequest->getClientVersion())
+            {
+                http_response_code(400);
+                print('Missing required header: ' . StandardHeaders::CLIENT_VERSION->value);
+                return false;
+            }
+
+            if(!$clientRequest->headerExists(StandardHeaders::PUBLIC_KEY))
+            {
+                http_response_code(400);
+                print('Missing required header: ' . StandardHeaders::PUBLIC_KEY->value);
+                return false;
+            }
+
+            if(!$clientRequest->headerExists(StandardHeaders::IDENTIFY_AS))
+            {
+                http_response_code(400);
+                print('Missing required header: ' . StandardHeaders::IDENTIFY_AS->value);
+                return false;
+            }
+
+            if(!Validator::validatePeerAddress($clientRequest->getHeader(StandardHeaders::IDENTIFY_AS)))
+            {
+                http_response_code(400);
+                print('Invalid Identify-As header: ' . $clientRequest->getHeader(StandardHeaders::IDENTIFY_AS));
+                return false;
+            }
+
+            return true;
+        }
+
         /**
          * Processes a client request to initiate a session. Validates required headers,
          * ensures the peer is authorized and enabled, and creates a new session UUID
@@ -80,58 +134,66 @@
          */
         private static function handleInitiateSession(ClientRequest $clientRequest): void
         {
-
+            if(!self::validateInitHeaders($clientRequest))
-            if(!$clientRequest->getClientName())
             {
-                http_response_code(400);
-                print('Missing required header: ' . StandardHeaders::CLIENT_NAME->value);
                 return;
             }
 
-            if(!$clientRequest->getClientVersion())
+            // We always accept the client's public key at first
-            {
+            $publicKey = $clientRequest->getHeader(StandardHeaders::PUBLIC_KEY);
-                http_response_code(400);
-                print('Missing required header: ' . StandardHeaders::CLIENT_VERSION->value);
-                return;
-            }
-
-            if(!$clientRequest->headerExists(StandardHeaders::PUBLIC_KEY))
-            {
-                http_response_code(400);
-                print('Missing required header: ' . StandardHeaders::PUBLIC_KEY->value);
-                return;
-            }
-
-            if(!$clientRequest->headerExists(StandardHeaders::IDENTIFY_AS))
-            {
-                http_response_code(400);
-                print('Missing required header: ' . StandardHeaders::IDENTIFY_AS->value);
-                return;
-            }
-
-            if(!Validator::validatePeerAddress($clientRequest->getHeader(StandardHeaders::IDENTIFY_AS)))
-            {
-                http_response_code(400);
-                print('Invalid Identify-As header: ' . $clientRequest->getHeader(StandardHeaders::IDENTIFY_AS));
-                return;
-            }
 
             // If the peer is identifying as the same domain
             if($clientRequest->getIdentifyAs()->getDomain() === Configuration::getInstanceConfiguration()->getDomain())
             {
                 // Prevent the peer from identifying as the host unless it's coming from an external domain
-               if($clientRequest->getIdentifyAs()->getUsername() === 'host')
+               if($clientRequest->getIdentifyAs()->getUsername() === ReservedUsernames::HOST->value)
                {
                      http_response_code(403);
                      print('Unauthorized: The requested peer is not allowed to identify as the host');
                      return;
                }
             }
+            // If the peer is identifying as an external domain
             else
             {
-                http_response_code(400);
+                // Only allow the host to identify as an external peer
-                print('External domains are not supported yet');
+                if($clientRequest->getIdentifyAs()->getUsername() !== ReservedUsernames::HOST->value)
-                return;
+                {
+                    http_response_code(403);
+                    print('Unauthorized: The requested peer is not allowed to identify as an external peer');
+                    return;
+                }
+
+                try
+                {
+                    // We need to obtain the public key of the host, since we can't trust the client
+                    $resolvedServer = ServerResolver::resolveDomain($clientRequest->getIdentifyAs()->getDomain());
+
+                    // Override the public key with the resolved server's public key
+                    $publicKey = $resolvedServer->getPublicKey();
+                }
+                catch (Exceptions\ResolutionException $e)
+                {
+                    Logger::getLogger()->error('Failed to resolve the host domain', $e);
+                    http_response_code(409);
+                    print('Conflict: Failed to resolve the host domain: ' . $e->getMessage());
+                    return;
+                }
+                catch (Exception $e)
+                {
+                    Logger::getLogger()->error('An internal error occurred while resolving the host domain', $e);
+                    http_response_code(500);
+                    if(Configuration::getSecurityConfiguration()->isDisplayInternalExceptions())
+                    {
+                        print(Utilities::throwableToString($e));
+                    }
+                    else
+                    {
+                        print('An internal error occurred');
+                    }
+
+                    return;
+                }
             }
 
             try
@@ -165,7 +227,7 @@
                 }
 
                 // Create the session UUID
-                $sessionUuid = SessionManager::createSession($clientRequest->getHeader(StandardHeaders::PUBLIC_KEY), $registeredPeer, $clientRequest->getClientName(), $clientRequest->getClientVersion());
+                $sessionUuid = SessionManager::createSession($publicKey, $registeredPeer, $clientRequest->getClientName(), $clientRequest->getClientVersion());
                 http_response_code(201); // Created
                 print($sessionUuid); // Return the session UUID
             }