test: add man-in-the-middle test for certificate verification

e2e/bats/assets/certificate/certificate.mo

@@ -0,0 +1,11 @@
+actor Certificate {
+
+    public query func hello_query(name: Text) : async Text {
+        "Hello, " # name # "!"
+    };
+
+    public func hello_update(name: Text) : async Text {
+        "Hello, " # name # "!"
+    }
+
+}

e2e/bats/assets/certificate/patch.bash

@@ -0,0 +1 @@
+dfx config canisters/certificate/main certificate.mo

e2e/bats/certificate.bash

@@ -0,0 +1,64 @@
+#!/usr/bin/env bats
+
+load utils/_
+
+setup() {
+    # We want to work from a temporary directory, different for every test.
+    cd $(mktemp -d -t dfx-e2e-XXXXXXXX)
+    export RUST_BACKTRACE=1
+
+    dfx_new certificate
+
+    install_asset certificate
+    dfx_start
+
+    dfx deploy
+
+    BACKEND=$(jq -r .networks.local.bind dfx.json)
+
+    # Sometimes, something goes wrong with mitmdump's initialization.
+    # It reports that it is listening, and the `nc` call succeeds,
+    # but it does not actually respond to requests.
+    #
+    # This happens whether using a fixed port or a dynamic port.
+    # For this reason, we retry initialization until `dfx ping` succeeds.
+    #
+    # I have seen this process take as many as 9 iterations to succeed,
+    # so across a large number of CI runs, it could take even more.
+    # The overall CI timeout will limit the maximum time taken.
+
+    while true
+    do
+        MITM_PORT=$(python3 ${BATS_TEST_DIRNAME}/utils/get_ephemeral_port.py)
+        cat <<<$(jq .networks.local.bind=\"127.0.0.1:$MITM_PORT\" dfx.json) >dfx.json
+
+        mitmdump -p $MITM_PORT --mode reverse:http://$BACKEND  --replace '/~s/Hello,/Hullo,' &
+        MITMDUMP_PID=$!
+
+        timeout 5 sh -c \
+            "until nc -z localhost $MITM_PORT; do echo waiting for mitmdump; sleep 1; done" \
+            || (echo "mitmdump did not start on port $MITM_PORT" && exit 1)
+
+        if timeout 10 dfx ping; then
+            break
+        fi
+
+        kill -9 $MITMDUMP_PID
+    done
+}
+
+teardown() {
+    kill -9 $MITMDUMP_PID
+
+    dfx_stop
+}
+
+@test "mitm attack - update: attack fails because certificate verification fails" {
+    assert_command_fail dfx canister call certificate hello_update '("Buckaroo")'
+    assert_match 'Certificate verification failed.'
+}
+
+@test "mitm attack - query: attack succeeds because there is no certificate to verify" {
+    assert_command dfx canister call certificate hello_query '("Buckaroo")'
+    assert_eq '("Hullo, Buckaroo!")'
+}

e2e/bats/default.nix

@@ -25,6 +25,7 @@ let
             gnutar
             gzip
             jq
+            mitmproxy
             netcat
             ps
             python3

e2e/bats/utils/get_ephemeral_port.py

@@ -0,0 +1,5 @@
+import socket
+
+with socket.socket() as s:
+  s.bind(('', 0))
+  print(s.getsockname()[1], end='')