Add the ability to disable signups, but allow signups from a whitelist

This feature can be enabled by setting SIGNUPS_ALLOWED=false and
providing a comma-separated list of whitelisted domains in
SIGNUPS_DOMAINS_WHITELIST.

Fixes #727

.env.template

@@ -95,6 +95,14 @@
 ## Controls if new users can register
 # SIGNUPS_ALLOWED=true
 
+## Controls if new users from a list of comma-separated domains can register
+## even if SIGNUPS_ALLOWED is set to false
+##
+## WARNING: There is currently no validation that prevents anyone from
+##          signing up with any made-up email address from one of these
+##          whitelisted domains!
+# SIGNUPS_DOMAINS_WHITELIST=example.com,example.net,example.org
+
 ## Token for the admin interface, preferably use a long random string
 ## One option is to use 'openssl rand -base64 48'
 ## If not set, the admin panel is disabled

src/api/core/accounts.rs

@@ -90,7 +90,7 @@ fn register(data: JsonUpcase<RegisterData>, conn: DbConn) -> EmptyResult {
             }
         }
         None => {
-            if CONFIG.signups_allowed() || Invitation::take(&data.Email, &conn) {
+            if CONFIG.signups_allowed() || Invitation::take(&data.Email, &conn) || CONFIG.can_signup_user(&data.Email) {
                 User::new(data.Email.clone())
             } else {
                 err!("Registration not allowed or user already exists")

src/config.rs

@@ -243,6 +243,8 @@ make_config! {
         disable_icon_download:  bool,   true,   def,    false;
         /// Allow new signups |> Controls if new users can register. Note that while this is disabled, users could still be invited
         signups_allowed:        bool,   true,   def,    true;
+        /// Allow signups only from this list of comma-separated domains
+        signups_domains_whitelist: String, true, def,   "".to_string();
         /// Allow invitations |> Controls whether users can be invited by organization admins, even when signups are disabled
         invitations_allowed:    bool,   true,   def,    true;
         /// Password iterations |> Number of server-side passwords hashing iterations.
@@ -491,6 +493,16 @@ impl Config {
         self.update_config(builder)
     }
 
+    pub fn can_signup_user(&self, email: &str) -> bool {
+        let e: Vec<&str> = email.rsplitn(2, "@").collect();
+        if e.len() != 2 || e[0].is_empty() || e[1].is_empty() {
+            warn!("Failed to parse email address '{}'", email);
+            return false
+        }
+        
+        self.signups_domains_whitelist().split(",").any(|d| d == e[0])
+    }
+
     pub fn delete_user_config(&self) -> Result<(), Error> {
         crate::util::delete_file(&CONFIG_FILE)?;