refactor: consolidate auth messages into client and user_agent packages

protobufs/user_agent.proto

@@ -1,10 +1,25 @@
 syntax = "proto3";
 
-package arbiter;
+package arbiter.user_agent;
 
-import "auth.proto";
 import "google/protobuf/empty.proto";
 
+message AuthChallengeRequest {
+  bytes pubkey = 1;
+  optional string bootstrap_token = 2;
+}
+
+message AuthChallenge {
+  bytes pubkey = 1;
+  int32 nonce = 2;
+}
+
+message AuthChallengeSolution {
+  bytes signature = 1;
+}
+
+message AuthOk {}
+
 message UnsealStart {
   bytes client_pubkey = 1;
 }
@@ -35,17 +50,19 @@ enum VaultState {
 
 message UserAgentRequest {
   oneof payload {
-    arbiter.auth.ClientMessage auth_message = 1;
-    UnsealStart unseal_start = 2;
-    UnsealEncryptedKey unseal_encrypted_key = 3;
-    google.protobuf.Empty query_vault_state = 4;
+    AuthChallengeRequest auth_challenge_request = 1;
+    AuthChallengeSolution auth_challenge_solution = 2;
+    UnsealStart unseal_start = 3;
+    UnsealEncryptedKey unseal_encrypted_key = 4;
+    google.protobuf.Empty query_vault_state = 5;
   }
 }
 message UserAgentResponse {
   oneof payload {
-    arbiter.auth.ServerMessage auth_message = 1;
-    UnsealStartResponse unseal_start_response = 2;
-    UnsealResult unseal_result = 3;
-    VaultState vault_state = 4;
+    AuthChallenge auth_challenge = 1;
+    AuthOk auth_ok = 2;
+    UnsealStartResponse unseal_start_response = 3;
+    UnsealResult unseal_result = 4;
+    VaultState vault_state = 5;
   }
 }