add request verification extractor

chat/migrations/20240116203402_init.sql

@@ -14,7 +14,7 @@ create table users (
     instance_id text not null references identity_instances (id) on delete cascade,
     remote_user_id text not null,
     username       text not null,
-    
+
     avatar text -- URL, not hash, as this is a remote file
 );
 
@@ -46,6 +46,14 @@ create table messages (
     channel_id text not null references channels (id) on delete cascade,
     author_id  text not null,
     updated_at timestamptz not null default now(),
-    
+
     content text not null
 );
+
+create table instance (
+    id integer not null primary key default 1,
+    public_key  text not null,
+    private_key text not null,
+
+    constraint singleton check (id = 1)
+);