Single sign-on is the only way in when it is configured

The sign-in page shows only the identity provider; password sign-in and
new local accounts are refused. Invites go through the identity provider.
Server 0.1.2, chart 0.1.3.

crates/server/src/pages.rs

@@ -215,24 +215,29 @@ async fn authorize_form(state: &AppState, q: &AuthorizeQuery, error: Option<&str
             .unwrap_or_default(),
     ]
     .concat();
-    // Single sign-on first when the server has it; the password form stays for local accounts.
-    let mut body = state
-        .oidc
-        .as_ref()
-        .map(|o| {
-            format!(
-                r#"<div class="card"><h2>Sign in for VS Code</h2>{}<a class="button" href="/oidc/start?{}">Sign in with {}</a></div>"#,
-                error_line(error),
-                escape(&q.to_query_string()),
-                escape(&o.config.label),
-            )
-        })
-        .unwrap_or_default();
-    let (title, error) = if body.is_empty() {
-        ("Sign in for VS Code", error)
-    } else {
-        ("Or with a password", None)
-    };
+    // With single sign-on the identity provider is the only way in: no
+    // password form, no new local accounts. An invite goes through it too.
+    if let Some(o) = &state.oidc {
+        let invited = match &q.invite {
+            Some(invite) => match state.store.invite_organisation(&auth::sha256(invite)).await {
+                Ok(Some((_, space_name))) => format!(
+                    r#"<p class="muted">You were invited to <b>{}</b>.</p>"#,
+                    escape(&space_name)
+                ),
+                _ => String::new(),
+            },
+            None => String::new(),
+        };
+        let body = format!(
+            r#"<div class="card"><h2>Sign in for VS Code</h2>{}{invited}<a class="button" href="/oidc/start?{}">Sign in with {}</a></div>"#,
+            error_line(error),
+            escape(&q.to_query_string()),
+            escape(&o.config.label),
+        );
+        return page(state, "Sign in", &body);
+    }
+    let mut body = String::new();
+    let title = "Sign in for VS Code";
     body.push_str(&format!(
         r#"<div class="card"><h2>{title}</h2>{}
 <form method="post" action="/authorize">{fields}{}
@@ -269,6 +274,10 @@ pub async fn authorize_submit(
     if check_authorize(&state, &q).is_err() {
         return authorize_form(&state, &q, None).await;
     }
+    if let Some(o) = &state.oidc {
+        let message = format!("This server signs in with {} only.", o.config.label);
+        return authorize_form(&state, &q, Some(&message)).await;
+    }
     let account = match form.action.as_str() {
         "signup" => sign_up(&state, &form).await,
         _ => sign_in(&state, &form).await,