diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..48bb61b
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+config.php
+vendor
diff --git a/.htaccess b/.htaccess
new file mode 100644
index 0000000..74b487f
--- /dev/null
+++ b/.htaccess
@@ -0,0 +1,5 @@
+Options -Indexes
+ErrorDocument 404 /404.html
+
+RewriteEngine On
+RewriteRule "^api/v1/(.+)$" "/api.php?path=$1" [L]
diff --git a/404.html b/404.html
new file mode 100644
index 0000000..6e3c541
--- /dev/null
+++ b/404.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>404 - No trobat</title>
+    <style>
+    html {
+      font-family: 'Roboto', 'Helvetica', 'Arial', sans-serif;
+    }
+    </style>
+  </head>
+  <body>
+    <h1>Error 404</h1>
+    <p>Ho sentim, però si cercaves existència i unicitat, ens sap greu informar-te que aquesta pàgina ni tan sols existeix :(</p>
+    <p>Potser, però, t'interesa fer-li una ullada a la <a href="https://dafme.upc.edu/ca/apunts">comi apunts</a>.</p>
+  </body>
+</html>
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..4edaf74
--- /dev/null
+++ b/README.md
@@ -0,0 +1,21 @@
+# DeleFME/covid-tracability-backend
+Per veure el repositori principal, aneu a [DeleFME/covid-tracability](https://github.com/DeleFME/covid-tracability).
+
+## Requisits
+- Servidor web Apache
+- MariaDB o MySQL
+- Composer
+
+## Instal·lació
+Per instal·lar el backend, seguiu els següents passos:
+
+1. Cloneu aquest repositori al directori arrel del vostre servidor web.
+2. Feu un duplicat de l'arxiu `config.default.php` amb el nom `config.php`, i ompliu el fitxer amb la configuració desitjada.
+3. [Instal·leu Composer](https://getcomposer.org/doc/00-intro.md) a la vostra màquina (si no el teniu ja instal·lat) i executeu la comanda `composer install` al directori arrel.
+4. Instal·leu la base de dades seguint els següents pasos:
+    a. A MariaDB/MySQL, executeu la següent comanda per inicialitzar la base de dades: `CREATE DATABASE covid_tracability CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;` (es pot substituir `covid_tracability` per un altre nom de la base de dades).
+    b. Executeu la comanda `mysql -u usuari -p covid_tracability < utils/db_structure.sql`, on `usuari` és l'usuari de MariaDB/MySQL.
+5. Configureu Apache perquè faci cas a l'arxiu `.htaccess` del directori arrel. \[[+ info sobre com fer-ho](https://askubuntu.com/questions/429869/is-this-a-correct-way-to-enable-htaccess-in-apache-2-4-7)\]
+6. Ja teniu el servidor disponible a `http://localhost/`!
+
+Nota: per tal d'utilitzar Apache amb diversos projectes, el que es pot fer és posar el repositori a un altre directori, i configurar un `virtualhost` que respongui les peticions d'un host com `covid-tracability-backend.test` servint els documents de l'altre directori. També s'hauria de configurar a l'arxiu [hosts](https://ca.wikipedia.org/wiki/Fitxer_de_hosts) la resolució d'aquest domini (`covid-tracability-backend.test`) a l'IP `172.0.0.1`.
diff --git a/api.php b/api.php
new file mode 100644
index 0000000..31c2b14
--- /dev/null
+++ b/api.php
@@ -0,0 +1,4 @@
+<?php
+require_once('core.php');
+
+DAFME\Covid\API::process((string)($_GET['path'] ?? ''));
diff --git a/composer.json b/composer.json
new file mode 100644
index 0000000..b9435c2
--- /dev/null
+++ b/composer.json
@@ -0,0 +1,10 @@
+{
+    "require": {
+        "google/apiclient": "^2.7"
+    },
+    "autoload": {
+        "psr-4": {
+            "DAFME\\Covid\\": "inc/"
+        }
+    }
+}
diff --git a/composer.lock b/composer.lock
new file mode 100644
index 0000000..ff0a193
--- /dev/null
+++ b/composer.lock
@@ -0,0 +1,868 @@
+{
+    "_readme": [
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+    ],
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+            "homepage": "http://github.com/Seldaek/monolog",
+            "keywords": [
+                "log",
+                "logging",
+                "psr-3"
+            ],
+            "funding": [
+                {
+                    "url": "https://github.com/Seldaek",
+                    "type": "github"
+                },
+                {
+                    "url": "https://tidelift.com/funding/github/packagist/monolog/monolog",
+                    "type": "tidelift"
+                }
+            ],
+            "time": "2020-07-23T08:41:23+00:00"
+        },
+        {
+            "name": "phpseclib/phpseclib",
+            "version": "2.0.29",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/phpseclib/phpseclib.git",
+                "reference": "497856a8d997f640b4a516062f84228a772a48a8"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/phpseclib/phpseclib/zipball/497856a8d997f640b4a516062f84228a772a48a8",
+                "reference": "497856a8d997f640b4a516062f84228a772a48a8",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.3.3"
+            },
+            "require-dev": {
+                "phing/phing": "~2.7",
+                "phpunit/phpunit": "^4.8.35|^5.7|^6.0",
+                "squizlabs/php_codesniffer": "~2.0"
+            },
+            "suggest": {
+                "ext-gmp": "Install the GMP (GNU Multiple Precision) extension in order to speed up arbitrary precision integer arithmetic operations.",
+                "ext-libsodium": "SSH2/SFTP can make use of some algorithms provided by the libsodium-php extension.",
+                "ext-mcrypt": "Install the Mcrypt extension in order to speed up a few other cryptographic operations.",
+                "ext-openssl": "Install the OpenSSL extension in order to speed up a wide variety of cryptographic operations."
+            },
+            "type": "library",
+            "autoload": {
+                "files": [
+                    "phpseclib/bootstrap.php"
+                ],
+                "psr-4": {
+                    "phpseclib\\": "phpseclib/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Jim Wigginton",
+                    "email": "terrafrost@php.net",
+                    "role": "Lead Developer"
+                },
+                {
+                    "name": "Patrick Monnerat",
+                    "email": "pm@datasphere.ch",
+                    "role": "Developer"
+                },
+                {
+                    "name": "Andreas Fischer",
+                    "email": "bantu@phpbb.com",
+                    "role": "Developer"
+                },
+                {
+                    "name": "Hans-Jürgen Petrich",
+                    "email": "petrich@tronic-media.com",
+                    "role": "Developer"
+                },
+                {
+                    "name": "Graham Campbell",
+                    "email": "graham@alt-three.com",
+                    "role": "Developer"
+                }
+            ],
+            "description": "PHP Secure Communications Library - Pure-PHP implementations of RSA, AES, SSH2, SFTP, X.509 etc.",
+            "homepage": "http://phpseclib.sourceforge.net",
+            "keywords": [
+                "BigInteger",
+                "aes",
+                "asn.1",
+                "asn1",
+                "blowfish",
+                "crypto",
+                "cryptography",
+                "encryption",
+                "rsa",
+                "security",
+                "sftp",
+                "signature",
+                "signing",
+                "ssh",
+                "twofish",
+                "x.509",
+                "x509"
+            ],
+            "funding": [
+                {
+                    "url": "https://github.com/terrafrost",
+                    "type": "github"
+                },
+                {
+                    "url": "https://www.patreon.com/phpseclib",
+                    "type": "patreon"
+                },
+                {
+                    "url": "https://tidelift.com/funding/github/packagist/phpseclib/phpseclib",
+                    "type": "tidelift"
+                }
+            ],
+            "time": "2020-09-08T04:24:43+00:00"
+        },
+        {
+            "name": "psr/cache",
+            "version": "1.0.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/php-fig/cache.git",
+                "reference": "d11b50ad223250cf17b86e38383413f5a6764bf8"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/php-fig/cache/zipball/d11b50ad223250cf17b86e38383413f5a6764bf8",
+                "reference": "d11b50ad223250cf17b86e38383413f5a6764bf8",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.3.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.0.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Psr\\Cache\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "PHP-FIG",
+                    "homepage": "http://www.php-fig.org/"
+                }
+            ],
+            "description": "Common interface for caching libraries",
+            "keywords": [
+                "cache",
+                "psr",
+                "psr-6"
+            ],
+            "time": "2016-08-06T20:24:11+00:00"
+        },
+        {
+            "name": "psr/http-client",
+            "version": "1.0.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/php-fig/http-client.git",
+                "reference": "2dfb5f6c5eff0e91e20e913f8c5452ed95b86621"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/php-fig/http-client/zipball/2dfb5f6c5eff0e91e20e913f8c5452ed95b86621",
+                "reference": "2dfb5f6c5eff0e91e20e913f8c5452ed95b86621",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^7.0 || ^8.0",
+                "psr/http-message": "^1.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.0.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Psr\\Http\\Client\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "PHP-FIG",
+                    "homepage": "http://www.php-fig.org/"
+                }
+            ],
+            "description": "Common interface for HTTP clients",
+            "homepage": "https://github.com/php-fig/http-client",
+            "keywords": [
+                "http",
+                "http-client",
+                "psr",
+                "psr-18"
+            ],
+            "time": "2020-06-29T06:28:15+00:00"
+        },
+        {
+            "name": "psr/http-message",
+            "version": "1.0.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/php-fig/http-message.git",
+                "reference": "f6561bf28d520154e4b0ec72be95418abe6d9363"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/php-fig/http-message/zipball/f6561bf28d520154e4b0ec72be95418abe6d9363",
+                "reference": "f6561bf28d520154e4b0ec72be95418abe6d9363",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.3.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.0.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Psr\\Http\\Message\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "PHP-FIG",
+                    "homepage": "http://www.php-fig.org/"
+                }
+            ],
+            "description": "Common interface for HTTP messages",
+            "homepage": "https://github.com/php-fig/http-message",
+            "keywords": [
+                "http",
+                "http-message",
+                "psr",
+                "psr-7",
+                "request",
+                "response"
+            ],
+            "time": "2016-08-06T14:39:51+00:00"
+        },
+        {
+            "name": "psr/log",
+            "version": "1.1.3",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/php-fig/log.git",
+                "reference": "0f73288fd15629204f9d42b7055f72dacbe811fc"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/php-fig/log/zipball/0f73288fd15629204f9d42b7055f72dacbe811fc",
+                "reference": "0f73288fd15629204f9d42b7055f72dacbe811fc",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.3.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.1.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Psr\\Log\\": "Psr/Log/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "PHP-FIG",
+                    "homepage": "http://www.php-fig.org/"
+                }
+            ],
+            "description": "Common interface for logging libraries",
+            "homepage": "https://github.com/php-fig/log",
+            "keywords": [
+                "log",
+                "psr",
+                "psr-3"
+            ],
+            "time": "2020-03-23T09:12:05+00:00"
+        },
+        {
+            "name": "ralouphie/getallheaders",
+            "version": "3.0.3",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/ralouphie/getallheaders.git",
+                "reference": "120b605dfeb996808c31b6477290a714d356e822"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/ralouphie/getallheaders/zipball/120b605dfeb996808c31b6477290a714d356e822",
+                "reference": "120b605dfeb996808c31b6477290a714d356e822",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.6"
+            },
+            "require-dev": {
+                "php-coveralls/php-coveralls": "^2.1",
+                "phpunit/phpunit": "^5 || ^6.5"
+            },
+            "type": "library",
+            "autoload": {
+                "files": [
+                    "src/getallheaders.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Ralph Khattar",
+                    "email": "ralph.khattar@gmail.com"
+                }
+            ],
+            "description": "A polyfill for getallheaders.",
+            "time": "2019-03-08T08:55:37+00:00"
+        }
+    ],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": [],
+    "prefer-stable": false,
+    "prefer-lowest": false,
+    "platform": [],
+    "platform-dev": [],
+    "plugin-api-version": "1.1.0"
+}
diff --git a/config.default.php b/config.default.php
new file mode 100644
index 0000000..7a5af80
--- /dev/null
+++ b/config.default.php
@@ -0,0 +1,31 @@
+<?php
+// App configuration
+
+$conf = [];
+
+// Nom de l'aplicatiu
+$conf['appName'] = 'App de traçabilitat DAFME';
+
+// Configuració de la base de dades
+$conf['db'] = [];
+$conf['db']['host'] = '';
+$conf['db']['database'] = '';
+$conf['db']['user'] = '';
+$conf['db']['password'] = '';
+
+// Enllaç al formulari de Google de l'FME
+$conf['formUrl'] = 'https://docs.google.com/forms/d/e/1FAIpQLSfT9o287VqLyhwR8LPdloAQWhuqCgA3NfdhgP5vb9_sVQHL-g/viewform';
+
+// Credencials de les APIs de Google (seguir pasos de
+// https://developers.google.com/identity/protocols/oauth2/web-server#creatingcred)
+$conf['goog'] = [];
+$conf['goog']['clientId'] = '';
+$conf['goog']['secret'] = '';
+
+// Lloc on s'allotja l'API (backend, és a dir, aquest programari)
+//   Exemple: https://covid-backend.fme.upc.edu/
+$conf['fullPath'] = '';
+
+// Lloc on s'allotja el web (frontend)
+//   Exemple: https://covid.fme.upc.edu/
+$conf['homeUrl'] = '';
diff --git a/core.php b/core.php
new file mode 100644
index 0000000..e58a7eb
--- /dev/null
+++ b/core.php
@@ -0,0 +1,22 @@
+<?php
+// core.php - El fitxer més elemental, estimat Watson
+
+// Get settings
+require(__DIR__.'/config.php');
+
+// Set composer
+require(__DIR__.'/vendor/autoload.php');
+
+// Set timezone and locale accordingly
+date_default_timezone_set('Europe/Madrid');
+
+// Connect to the DB
+$con = new PDO('mysql:host='.$conf['db']['host'].';dbname='.$conf['db']['database'].';charset=utf8mb4', $conf['db']['user'], $conf['db']['password']);
+
+// Session settings
+session_set_cookie_params([
+  'lifetime' => 0,
+  'path' => ($conf['path'] ?? '/'),
+  'httponly' => true
+]);
+session_start();
diff --git a/inc/API.php b/inc/API.php
new file mode 100644
index 0000000..0d5530e
--- /dev/null
+++ b/inc/API.php
@@ -0,0 +1,104 @@
+<?php
+namespace DAFME\Covid;
+
+class API {
+  private static function returnJSON($array) {
+    echo json_encode($array);
+  }
+
+  public static function returnError($errorMessage = 'Unexpected error') {
+    http_response_code(400);
+    self::returnJson([
+      'status' => 'error',
+      'errorMessage' =>  $errorMessage
+    ]);
+  }
+
+  public static function returnPayload($payload) {
+    self::returnJson([
+      'status' => 'ok',
+      'payload' => $payload
+    ]);
+  }
+
+  public static function returnOk() {
+    self::returnJson([
+      'status' => 'ok'
+    ]);
+  }
+
+  private static function checkSignInStatus() {
+    if (!Users::isSignedIn()) {
+      self::returnError('The user hasn\'t signed in.');
+      exit();
+    }    
+  }
+
+  public static function process($path) {
+    global $conf;
+
+    header('Content-Type: application/json');
+
+    if (isset($conf['frontendUrl']) && !empty($conf['frontendUrl']))
+      header('Access-Control-Allow-Origin: '.$conf['frontendUrl']);
+
+    $parts = explode('/', $path);
+    $method = $parts[0] ?? '';
+
+    switch ($method) {
+      case 'getAuthUrl':
+        $auth = new Auth();
+        self::returnPayload([
+          'url' => $auth->getAuthUrl()
+        ]);
+        break;
+
+      case 'isSignedIn':
+        $isSignedIn = \DAFME\Covid\Users::isSignedIn();
+        self::returnPayload([
+          'signedIn' => $isSignedIn
+        ]);
+        break;
+
+      case 'signOut':
+        \DAFME\Covid\Users::signOut();
+        self::returnOk();
+        break;
+
+      case 'getAllSubjects':
+        $subjects = Subjects::getAll();
+
+        if ($subjects === false)
+          self::returnError();
+
+        self::returnPayload([
+          'subjects' => $subjects
+        ]);
+        break;
+
+      case 'getUserSubjects':
+        self::checkSignInStatus();
+        // @TODO: Implement this method
+        break;
+
+      case 'setUserSubjects':
+        self::checkSignInStatus();
+        // @TODO: Implement this method
+        break;
+
+      case 'getClasses':
+        self::checkSignInStatus();
+        // @TODO: Implement this method
+        break;
+
+      case 'setClassState':
+        self::checkSignInStatus();
+        // @TODO: Handle this method
+        break;
+
+      default:
+        self::returnError('The method requested doesn\'t exist.');
+        break;
+    }
+  }
+}
diff --git a/inc/Auth.php b/inc/Auth.php
new file mode 100644
index 0000000..c0fc078
--- /dev/null
+++ b/inc/Auth.php
@@ -0,0 +1,59 @@
+<?php
+namespace DAFME\Covid;
+
+class Auth {
+  private $client;
+
+  public function __construct() {
+    global $conf;
+    $this->client = new \Google_Client();
+    $this->client->setApplicationName = 'dafme-covid-tracability-backend';
+    $this->client->setClientId($conf['goog']['clientId']);
+    $this->client->setClientSecret($conf['goog']['secret']);
+    $this->client->addScope('https://www.googleapis.com/auth/userinfo.email');
+    $this->client->setRedirectUri($conf['fullPath'].'oauth2callback.php');
+    $this->client->setAccessType('online');
+  }
+
+  public function getAuthUrl() {
+    return $this->client->createAuthUrl();
+  }
+
+  public function handleCallback() {
+    global $_GET, $con;
+    if (isset($_GET['error']) || !isset($_GET['code'])) return 1;
+
+    $accessToken = null;
+
+    try {
+      $accessToken = $this->client->fetchAccessTokenWithAuthCode($_GET['code']);
+    } catch (\Exception $exception) {
+      return 2;
+    }
+
+    $id = $this->client->verifyIdToken();
+    if ($id === false)
+      return 3;
+
+    if (!isset($id['sub']) || !isset($id['email']) || !isset($id['email_verified']))
+      return 4;
+
+    if ($id['email_verified'] === false)
+      return 5;
+
+    $sub = $id['sub'];
+    $email = $id['email'];
+
+    if (preg_match('/upc.edu$/', $id['email']) !== 1)
+      return 6;
+
+    if (!Users::signIn($sub, $email))
+      return 7;
+
+    return 0;
+  }
+
+  public function setAccessToken($token) {
+    $this->client->setAccessToken($token);
+  }
+}
diff --git a/inc/Subjects.php b/inc/Subjects.php
new file mode 100644
index 0000000..4d2cfdb
--- /dev/null
+++ b/inc/Subjects.php
@@ -0,0 +1,14 @@
+<?php
+namespace DAFME\Covid;
+
+class Subjects {
+  public static function getAll() {
+    global $con;
+    $query = $con->prepare('SELECT * FROM subjects');
+
+    if (!$query->execute())
+      return false;
+
+    return $query->fetchAll(\PDO::FETCH_ASSOC);
+  }
+}
diff --git a/inc/Users.php b/inc/Users.php
new file mode 100644
index 0000000..7679e04
--- /dev/null
+++ b/inc/Users.php
@@ -0,0 +1,51 @@
+<?php
+namespace DAFME\Covid;
+
+class Users {
+  private static function getUserId($sub) {
+    global $con;
+    $query = $con->prepare('SELECT id FROM users WHERE sub = ?');
+    if (!$query->execute([$sub]))
+      return false;
+
+    if ($query->rowCount() < 1)
+      return false;
+
+    $row = $query->fetch();
+    return $row['id'] ?? false;
+  }
+
+  public static function add($sub, $email) {
+    global $con;
+    $query = $con->prepare('INSERT INTO users (sub, email) VALUES (?, ?)');
+    if (!$query->execute([$sub, $email]))
+      return false;
+
+    return $con->lastInsertId();
+  }
+
+  public static function signIn($sub, $email) {
+    global $_SESSION;
+
+    $userId = self::getUserId($sub);
+
+    if ($userId === false)
+      $userId = self::add($sub, $email);
+
+    if ($userId === false)
+      return false;
+
+    $_SESSION['userId'] = $userId;
+    return true;
+  }
+
+  public static function signOut() {
+    global $_SESSION;
+    unset($_SESSION['userId']);
+  }
+
+  public static function isSignedIn() {
+    global $_SESSION;
+    return isset($_SESSION['userId']);
+  }
+}
diff --git a/oauth2callback.php b/oauth2callback.php
new file mode 100644
index 0000000..bf059bd
--- /dev/null
+++ b/oauth2callback.php
@@ -0,0 +1,33 @@
+<?php
+// Oauth2 callback, which is meant to complete the sign in process
+
+require_once('core.php');
+header('Content-Type: text/plain');
+
+$auth = new DAFME\Covid\Auth();
+$returnCode = $auth->handleCallback();
+
+switch ($returnCode) {
+  case 0:
+    header('Location: '.$conf['frontendUrl']);
+    break;
+
+  case 1:
+    echo 'Hi ha hagut un problema iniciant sessió. Probablement has denegat l\'inici de sessió.';
+    break;
+
+  case 2:
+  case 3:
+  case 4:
+  case 7:
+    echo 'Hi ha hagut un problema iniciant sessió. Sisplau prova de fer-ho de nou.';
+    break;
+
+  case 5:
+    echo 'El correu electrònic del teu compte no està verificat. Verifica\'l i torna a iniciar sessió';
+    break;
+
+  case 6:
+    echo 'El teu compte no pertany a la UPC. Sisplau, inicia sessió amb el teu compte de Google de la UPC.';
+    break;
+}
diff --git a/utils/db_structure.sql b/utils/db_structure.sql
new file mode 100644
index 0000000..cedf7a6
--- /dev/null
+++ b/utils/db_structure.sql
@@ -0,0 +1,24 @@
+-- SQL sentences to set up all the DB tables
+
+CREATE TABLE users (
+  id INT NOT NULL AUTO_INCREMENT,
+  PRIMARY KEY(id),
+  sub VARCHAR(255) NOT NULL UNIQUE,
+  email VARCHAR(320)
+);
+
+CREATE TABLE subjects (
+  id INT NOT NULL AUTO_INCREMENT,
+  PRIMARY KEY(id),
+  friendly_name VARCHAR(100) NOT NULL UNIQUE, -- Nom que es mostra al web
+  calendar_name VARCHAR(100) NOT NULL -- Nom al calendari de la FME
+);
+
+CREATE TABLE user_subjects (
+  id INT NOT NULL AUTO_INCREMENT,
+  PRIMARY KEY(id),
+  user_id INT NOT NULL,
+  subject_id INT NOT NULL
+);
+
+-- @TODO: Add form completion log table