add protocol to aggregator api config/capabilities (#1743)

* add dap_versions to aggregator api config/capabilities

* dap_version not dap_versions

* s/dap_version/protocol/ because the value includes `dap` and therefore is redundant

* dap-07

aggregator_api/src/models.rs

@@ -23,6 +23,7 @@ pub(crate) enum AggregatorRole {
 
 #[derive(Serialize, PartialEq, Eq, Debug)]
 pub(crate) struct AggregatorApiConfig {
+    pub protocol: &'static str,
     pub dap_url: Url,
     pub role: AggregatorRole,
     pub vdafs: Vec<SupportedVdaf>,

aggregator_api/src/routes.rs

@@ -33,6 +33,7 @@ pub(super) async fn get_config(
     State(config): State<Arc<Config>>,
 ) -> Json<AggregatorApiConfig> {
     Json(AggregatorApiConfig {
+        protocol: "DAP-07",
         dap_url: config.public_dap_url.clone(),
         role: AggregatorRole::Either,
         vdafs: vec![

aggregator_api/src/tests.rs

@@ -82,7 +82,7 @@ async fn get_config() {
             .await,
         Status::Ok,
         concat!(
-            r#"{"dap_url":"https://dap.url/","role":"Either","vdafs":"#,
+            r#"{"protocol":"DAP-07","dap_url":"https://dap.url/","role":"Either","vdafs":"#,
             r#"["Prio3Count","Prio3Sum","Prio3Histogram","Prio3CountVec","Prio3SumVec"],"#,
             r#""query_types":["TimeInterval","FixedSize"]}"#
         )