proto: add AuthRegister and AuthApprove RPCs

Add gRPC service definitions for managing auth requests:
AuthRegister to register interactive auth sessions and
AuthApprove/AuthReject to approve or deny pending requests
(used for SSH check mode).

Updates #1850

proto/headscale/v1/auth.proto

@@ -0,0 +1,26 @@
+syntax = "proto3";
+package headscale.v1;
+option go_package = "github.com/juanfont/headscale/gen/go/v1";
+
+import "headscale/v1/node.proto";
+
+message AuthRegisterRequest {
+  string user = 1;
+  string auth_id = 2;
+}
+
+message AuthRegisterResponse {
+  Node node = 1;
+}
+
+message AuthApproveRequest {
+  string auth_id = 1;
+}
+
+message AuthApproveResponse {}
+
+message AuthRejectRequest {
+  string auth_id = 1;
+}
+
+message AuthRejectResponse {}

proto/headscale/v1/headscale.proto

@@ -8,6 +8,7 @@ import "headscale/v1/user.proto";
 import "headscale/v1/preauthkey.proto";
 import "headscale/v1/node.proto";
 import "headscale/v1/apikey.proto";
+import "headscale/v1/auth.proto";
 import "headscale/v1/policy.proto";
 
 service HeadscaleService {
@@ -139,6 +140,29 @@ service HeadscaleService {
 
   // --- Node end ---
 
+  // --- Auth start ---
+  rpc AuthRegister(AuthRegisterRequest) returns (AuthRegisterResponse) {
+    option (google.api.http) = {
+      post : "/api/v1/auth/register"
+      body : "*"
+    };
+  }
+
+  rpc AuthApprove(AuthApproveRequest) returns (AuthApproveResponse) {
+    option (google.api.http) = {
+      post : "/api/v1/auth/approve"
+      body : "*"
+    };
+  }
+
+  rpc AuthReject(AuthRejectRequest) returns (AuthRejectResponse) {
+    option (google.api.http) = {
+      post : "/api/v1/auth/reject"
+      body : "*"
+    };
+  }
+  // --- Auth end ---
+
   // --- ApiKeys start ---
   rpc CreateApiKey(CreateApiKeyRequest) returns (CreateApiKeyResponse) {
     option (google.api.http) = {