Allow adding connect-src entries

.env.template

@@ -410,6 +410,14 @@
 ## Multiple values must be separated with a whitespace.
 # ALLOWED_IFRAME_ANCESTORS=
 
+## Allowed connect-src (Know the risks!)
+## https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/connect-src
+## Allows other domains to URLs which can be loaded using script interfaces like the Forwarded email alias feature
+## This adds the configured value to the 'Content-Security-Policy' headers 'connect-src' value.
+## Multiple values must be separated with a whitespace. And only HTTPS values are allowed.
+## Example: "https://my-addy-io.domain.tld https://my-simplelogin.domain.tld"
+# ALLOWED_CONNECT_SRC=""
+
 ## Number of seconds, on average, between login requests from the same IP address before rate limiting kicks in.
 # LOGIN_RATELIMIT_SECONDS=60
 ## Allow a burst of requests of up to this size, while maintaining the average indicated by `LOGIN_RATELIMIT_SECONDS`.

src/config.rs

@@ -238,6 +238,7 @@ macro_rules! make_config {
                 // Besides Pass, only String types will be masked via _privacy_mask.
                 const PRIVACY_CONFIG: &[&str] = &[
                     "allowed_iframe_ancestors",
+                    "allowed_connect_src",
                     "database_url",
                     "domain_origin",
                     "domain_path",
@@ -610,6 +611,9 @@ make_config! {
         /// Allowed iframe ancestors (Know the risks!) |> Allows other domains to embed the web vault into an iframe, useful for embedding into secure intranets
         allowed_iframe_ancestors: String, true, def,    String::new();
 
+        /// Allowed connect-src (Know the risks!) |> Allows other domains to URLs which can be loaded using script interfaces like the Forwarded email alias feature
+        allowed_connect_src:      String, true, def,    String::new();
+
         /// Seconds between login requests |> Number of seconds, on average, between login and 2FA requests from the same IP address before rate limiting kicks in
         login_ratelimit_seconds:       u64, false, def, 60;
         /// Max burst size for login requests |> Allow a burst of requests of up to this size, while maintaining the average indicated by `login_ratelimit_seconds`. Note that this applies to both the login and the 2FA, so it's recommended to allow a burst size of at least 2
@@ -761,6 +765,13 @@ fn validate_config(cfg: &ConfigItems) -> Result<(), Error> {
         );
     }
 
+    let connect_src = cfg.allowed_connect_src.to_lowercase();
+    for url in connect_src.split_whitespace() {
+        if !url.starts_with("https://") || Url::parse(url).is_err() {
+            err!("ALLOWED_CONNECT_SRC variable contains one or more invalid URLs. Only FQDN's starting with https are allowed");
+        }
+    }
+
     let whitelist = &cfg.signups_domains_whitelist;
     if !whitelist.is_empty() && whitelist.split(',').any(|d| d.trim().is_empty()) {
         err!("`SIGNUPS_DOMAINS_WHITELIST` contains empty tokens");

src/util.rs

@@ -98,10 +98,11 @@ impl Fairing for AppHeaders {
                   https://app.addy.io/api/ \
                   https://api.fastmail.com/ \
                   https://api.forwardemail.net \
-                  ;\
+                  {allowed_connect_src};\
                 ",
                 icon_service_csp = CONFIG._icon_service_csp(),
-                allowed_iframe_ancestors = CONFIG.allowed_iframe_ancestors()
+                allowed_iframe_ancestors = CONFIG.allowed_iframe_ancestors(),
+                allowed_connect_src = CONFIG.allowed_connect_src(),
             );
             res.set_raw_header("Content-Security-Policy", csp);
             res.set_raw_header("X-Frame-Options", "SAMEORIGIN");