crypto: Add settings to customize SAS accepting

Offer specifying settings to SAS accept() requests to limit the allowed
verification methods.

matrix_sdk/src/sas.rs

@@ -12,7 +12,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use matrix_sdk_base::crypto::{OutgoingVerificationRequest, ReadOnlyDevice, Sas as BaseSas};
+use matrix_sdk_base::crypto::{
+    AcceptSettings, OutgoingVerificationRequest, ReadOnlyDevice, Sas as BaseSas,
+};
 
 use crate::{error::Result, Client};
 
@@ -26,7 +28,14 @@ pub struct Sas {
 impl Sas {
     /// Accept the interactive verification flow.
     pub async fn accept(&self) -> Result<()> {
-        if let Some(req) = self.inner.accept() {
+        self.accept_with_settings(Default::default()).await
+    }
+
+    /// Accept the interactive verification flow with specific settings.
+    ///
+    /// Pass `settings` to customizes the accept-request before sending it.
+    pub async fn accept_with_settings(&self, settings: AcceptSettings) -> Result<()> {
+        if let Some(req) = self.inner.accept_with_settings(settings) {
             match req {
                 OutgoingVerificationRequest::ToDevice(r) => {
                     self.client.send_to_device(&r).await?;

matrix_sdk_crypto/src/lib.rs

@@ -55,4 +55,4 @@ pub use requests::{
     OutgoingVerificationRequest, RoomMessageRequest, ToDeviceRequest,
 };
 pub use store::CryptoStoreError;
-pub use verification::{Sas, VerificationRequest};
+pub use verification::{AcceptSettings, Sas, VerificationRequest};

matrix_sdk_crypto/src/verification/mod.rs

@@ -18,7 +18,7 @@ mod sas;
 
 pub use machine::VerificationMachine;
 pub use requests::VerificationRequest;
-pub use sas::{Sas, VerificationResult};
+pub use sas::{AcceptSettings, Sas, VerificationResult};
 
 #[cfg(test)]
 pub(crate) mod test {

matrix_sdk_crypto/src/verification/sas/mod.rs

@@ -27,8 +27,12 @@ use tracing::{error, info, trace, warn};
 use matrix_sdk_common::{
     api::r0::keys::upload_signatures::Request as SignatureUploadRequest,
     events::{
-        key::verification::cancel::CancelCode, AnyMessageEvent, AnyMessageEventContent,
-        AnyToDeviceEvent, AnyToDeviceEventContent,
+        key::verification::{
+            accept::{AcceptEventContent, AcceptMethod, AcceptToDeviceEventContent},
+            cancel::CancelCode,
+            ShortAuthenticationString,
+        },
+        AnyMessageEvent, AnyMessageEventContent, AnyToDeviceEvent, AnyToDeviceEventContent,
     },
     identifiers::{DeviceId, EventId, RoomId, UserId},
     uuid::Uuid,
@@ -253,7 +257,24 @@ impl Sas {
     /// This does nothing if the verification was already accepted, otherwise it
     /// returns an `AcceptEventContent` that needs to be sent out.
     pub fn accept(&self) -> Option<OutgoingVerificationRequest> {
-        self.inner.lock().unwrap().accept().map(|c| match c {
+        self.accept_with_settings(Default::default())
+    }
+
+    /// Accept the SAS verification customizing the accept method.
+    ///
+    /// This does nothing if the verification was already accepted, otherwise it
+    /// returns an `AcceptEventContent` that needs to be sent out.
+    ///
+    /// Specify a function modifying the attributes of the accept request.
+    pub fn accept_with_settings(
+        &self,
+        settings: AcceptSettings,
+    ) -> Option<OutgoingVerificationRequest> {
+        self.inner
+            .lock()
+            .unwrap()
+            .accept()
+            .map(|c| match settings.apply(c) {
                 AcceptContent::ToDevice(c) => {
                     let content = AnyToDeviceEventContent::KeyVerificationAccept(c);
                     self.content_to_request(content).into()
@@ -654,6 +675,55 @@ impl Sas {
     }
 }
 
+/// Customize the accept-reply for a verification process
+#[derive(Debug)]
+pub struct AcceptSettings {
+    allowed_methods: Vec<ShortAuthenticationString>,
+}
+
+impl Default for AcceptSettings {
+    fn default() -> Self {
+        Self {
+            allowed_methods: vec![
+                ShortAuthenticationString::Decimal,
+                ShortAuthenticationString::Emoji,
+            ],
+        }
+    }
+}
+
+impl AcceptSettings {
+    /// Create settings with exactly the specified SAS methods
+    pub fn with_allowed_methods(methods: Vec<ShortAuthenticationString>) -> Self {
+        Self {
+            allowed_methods: methods,
+        }
+    }
+
+    fn apply(self, mut content: AcceptContent) -> AcceptContent {
+        match &mut content {
+            AcceptContent::ToDevice(AcceptToDeviceEventContent {
+                method: AcceptMethod::MSasV1(c),
+                ..
+            }) => {
+                c.short_authentication_string = self.allowed_methods;
+                content
+            }
+            AcceptContent::Room(
+                _,
+                AcceptEventContent {
+                    method: AcceptMethod::MSasV1(c),
+                    ..
+                },
+            ) => {
+                c.short_authentication_string = self.allowed_methods;
+                content
+            }
+            _ => content,
+        }
+    }
+}
+
 #[cfg(test)]
 mod test {
     use std::{convert::TryFrom, sync::Arc};