[#414] ir/control: Implement service server

Implement `ControlServiceServer` on `Server` type. The `Server` requires all
requests to be signed with keys from the so-called whitelist. To obtain
health status, it uses the abstraction in the form of `HealthChecker`
interface.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/services/control/ir/server/server.go

@@ -0,0 +1,55 @@
+package control
+
+import (
+	"fmt"
+
+	crypto "github.com/nspcc-dev/neofs-crypto"
+)
+
+// Server is an entity that serves
+// Control service on IR node.
+//
+// To gain access to the service, any request must be
+// signed with a key from the white list.
+type Server struct {
+	prm Prm
+
+	allowedKeys [][]byte
+}
+
+func panicOnPrmValue(n string, v interface{}) {
+	const invalidPrmValFmt = "invalid %s parameter (%T): %v"
+	panic(fmt.Sprintf(invalidPrmValFmt, n, v, v))
+}
+
+// New creates a new instance of the Server.
+//
+// Panics if:
+//  - parameterized private key is nil;
+//  - parameterized HealthChecker is nil.
+//
+// Forms white list from all keys specified via
+// WithAllowedKeys option and a public key of
+// the parameterized private key.
+func New(prm Prm, opts ...Option) *Server {
+	// verify required parameters
+	switch {
+	case prm.key == nil:
+		panicOnPrmValue("key", prm.key)
+	case prm.healthChecker == nil:
+		panicOnPrmValue("health checker", prm.healthChecker)
+	}
+
+	// compute optional parameters
+	o := defaultOptions()
+
+	for _, opt := range opts {
+		opt(o)
+	}
+
+	return &Server{
+		prm: prm,
+
+		allowedKeys: append(o.allowedKeys, crypto.MarshalPublicKey(&prm.key.PublicKey)),
+	}
+}