Add block_on_origin_mismatch option to middleware (#287)

Co-authored-by: CapableWeb <capableweb@domain.com>
Co-authored-by: Rob Ede <robjtede@icloud.com>

actix-cors/src/builder.rs

@@ -102,6 +102,7 @@ impl Cors {
             send_wildcard: false,
             supports_credentials: true,
             vary_header: true,
+            block_on_origin_mismatch: true,
         };
 
         Cors {
@@ -448,6 +449,24 @@ impl Cors {
 
         self
     }
+
+    /// Configures whether requests should be pre-emptively blocked on mismatched origin.
+    ///
+    /// If `true`, a 400 Bad Request is returned immediately when a request fails origin validation.
+    ///
+    /// If `false`, the request will be processed as normal but relevant CORS headers will not be
+    /// appended to the response. In this case, the browser is trusted to validate CORS headers and
+    /// and block requests based on pre-flight requests. Use this setting to allow cURL and other
+    /// non-browser HTTP clients to function as normal, no matter what `Origin` the request has.
+    ///
+    /// Defaults to `true`.
+    pub fn block_on_origin_mismatch(mut self, block: bool) -> Cors {
+        if let Some(cors) = cors(&mut self.inner, &self.error) {
+            cors.block_on_origin_mismatch = block
+        }
+
+        self
+    }
 }
 
 impl Default for Cors {
@@ -474,6 +493,7 @@ impl Default for Cors {
             send_wildcard: false,
             supports_credentials: false,
             vary_header: true,
+            block_on_origin_mismatch: true,
         };
 
         Cors {

actix-cors/src/inner.rs

@@ -65,16 +65,19 @@ pub(crate) struct Inner {
     pub(crate) send_wildcard: bool,
     pub(crate) supports_credentials: bool,
     pub(crate) vary_header: bool,
+    pub(crate) block_on_origin_mismatch: bool,
 }
 
 static EMPTY_ORIGIN_SET: Lazy<HashSet<HeaderValue>> = Lazy::new(HashSet::new);
 
 impl Inner {
-    pub(crate) fn validate_origin(&self, req: &RequestHead) -> Result<(), CorsError> {
+    /// The bool returned in Ok(_) position indicates whether the `Access-Control-Allow-Origin`
+    /// header should be added to the response or not.
+    pub(crate) fn validate_origin(&self, req: &RequestHead) -> Result<bool, CorsError> {
         // return early if all origins are allowed or get ref to allowed origins set
         #[allow(clippy::mutable_key_type)]
         let allowed_origins = match &self.allowed_origins {
-            AllOrSome::All if self.allowed_origins_fns.is_empty() => return Ok(()),
+            AllOrSome::All if self.allowed_origins_fns.is_empty() => return Ok(true),
             AllOrSome::Some(allowed_origins) => allowed_origins,
             // only function origin validators are defined
             _ => &EMPTY_ORIGIN_SET,
@@ -85,9 +88,11 @@ impl Inner {
             // origin header exists and is a string
             Some(origin) => {
                 if allowed_origins.contains(origin) || self.validate_origin_fns(origin, req) {
-                    Ok(())
-                } else {
+                    Ok(true)
+                } else if self.block_on_origin_mismatch {
                     Err(CorsError::OriginNotAllowed)
+                } else {
+                    Ok(false)
                 }
             }
 

actix-cors/src/middleware.rs

@@ -16,7 +16,7 @@ use log::debug;
 use crate::{
     builder::intersperse_header_values,
     inner::{add_vary_header, header_value_try_into_method},
-    AllOrSome, Inner,
+    AllOrSome, CorsError, Inner,
 };
 
 /// Service wrapper for Cross-Origin Resource Sharing support.
@@ -60,9 +60,14 @@ impl<S> CorsMiddleware<S> {
     fn handle_preflight(&self, req: ServiceRequest) -> ServiceResponse {
         let inner = Rc::clone(&self.inner);
 
+        match inner.validate_origin(req.head()) {
+            Ok(true) => {}
+            Ok(false) => return req.error_response(CorsError::OriginNotAllowed),
+            Err(err) => return req.error_response(err),
+        };
+
         if let Err(err) = inner
-            .validate_origin(req.head())
-            .and_then(|_| inner.validate_allowed_method(req.head()))
+            .validate_allowed_method(req.head())
             .and_then(|_| inner.validate_allowed_headers(req.head()))
         {
             return req.error_response(err);
@@ -108,11 +113,17 @@ impl<S> CorsMiddleware<S> {
         req.into_response(res)
     }
 
-    fn augment_response<B>(inner: &Inner, mut res: ServiceResponse<B>) -> ServiceResponse<B> {
-        if let Some(origin) = inner.access_control_allow_origin(res.request().head()) {
-            res.headers_mut()
-                .insert(header::ACCESS_CONTROL_ALLOW_ORIGIN, origin);
-        };
+    fn augment_response<B>(
+        inner: &Inner,
+        origin_allowed: bool,
+        mut res: ServiceResponse<B>,
+    ) -> ServiceResponse<B> {
+        if origin_allowed {
+            if let Some(origin) = inner.access_control_allow_origin(res.request().head()) {
+                res.headers_mut()
+                    .insert(header::ACCESS_CONTROL_ALLOW_ORIGIN, origin);
+            };
+        }
 
         if let Some(ref expose) = inner.expose_headers_baked {
             log::trace!("exposing selected headers: {:?}", expose);
@@ -182,8 +193,10 @@ where
         }
 
         // only check actual requests with a origin header
-        if origin.is_some() {
-            if let Err(err) = self.inner.validate_origin(req.head()) {
+        let origin_allowed = match (origin, self.inner.validate_origin(req.head())) {
+            (None, _) => false,
+            (_, Ok(origin_allowed)) => origin_allowed,
+            (_, Err(err)) => {
                 debug!("origin validation failed; inner service is not called");
                 let mut res = req.error_response(err);
 
@@ -193,14 +206,14 @@ where
 
                 return ok(res.map_into_right_body()).boxed_local();
             }
-        }
+        };
 
         let inner = Rc::clone(&self.inner);
         let fut = self.service.call(req);
 
         Box::pin(async move {
             let res = fut.await;
-            Ok(Self::augment_response(&inner, res?).map_into_left_body())
+            Ok(Self::augment_response(&inner, origin_allowed, res?).map_into_left_body())
         })
     }
 }