diff --git a/src/authd.cr b/src/authd.cr
index 7d2575d..f59c2ec 100644
--- a/src/authd.cr
+++ b/src/authd.cr
@@ -9,12 +9,14 @@ require "./group.cr"
 module AuthD
 	enum RequestTypes
 		GET_TOKEN
+		ADD_USER
 	end
 
 	enum ResponseTypes
 		OK
 		MALFORMED_REQUEST
 		INVALID_CREDENTIALS
+		INVALID_USER
 	end
 
 	class GetTokenRequest
@@ -25,6 +27,17 @@ module AuthD
 		})
 	end
 
+	class AddUserRequest
+		JSON.mapping({
+			login: String,
+			password: String,
+			uid: Int32?,
+			gid: Int32?,
+			home: String?,
+			shell: String?
+		})
+	end
+
 	class Client < IPC::Client
 		property key : String
 
@@ -49,6 +62,10 @@ module AuthD
 			end
 		end
 
+		def send(type : RequestTypes, payload)
+			send type.value.to_u8, payload
+		end
+
 		def decode_token(token)
 			user, meta = JWT.decode token, @key, "HS256"
 
@@ -56,6 +73,24 @@ module AuthD
 
 			{user, meta}
 		end
+
+		# FIXME: Extra options may be useful to implement here.
+		def add_user(login : String, password : String) : AuthD::User | Exception
+			send RequestTypes::ADD_USER, {
+				:login => login,
+				:password => password
+			}.to_json
+
+			response = read
+
+			pp! response.type
+			case ResponseTypes.new response.type.to_i
+			when ResponseTypes::OK
+				AuthD::User.from_json response.payload
+			else
+				Exception.new response.payload
+			end
+		end
 	end
 end
 
diff --git a/src/main.cr b/src/main.cr
index b49d068..c968cde 100644
--- a/src/main.cr
+++ b/src/main.cr
@@ -13,6 +13,12 @@ require "./passwd.cr"
 
 extend AuthD
 
+class IPC::RemoteClient
+	def send(type : ResponseTypes, payload : String)
+		send type.value.to_u8, payload
+	end
+end
+
 authd_passwd_file = "passwd"
 authd_group_file = "group"
 authd_jwt_key = "nico-nico-nii"
@@ -69,6 +75,24 @@ IPC::Service.new "auth" do |event|
 
 			client.send ResponseTypes::OK.value.to_u8,
 				JWT.encode user.to_h, authd_jwt_key, "HS256"
+		when RequestTypes::ADD_USER
+			begin
+				request = AddUserRequest.from_json payload
+			rescue e
+				client.send ResponseTypes::MALFORMED_REQUEST.value.to_u8, e.message || ""
+
+				next
+			end
+
+			if passwd.user_exists? request.login
+				client.send ResponseTypes::INVALID_USER, "Another user with the same login already exists."
+
+				next
+			end
+
+			user = passwd.add_user request.login, request.password
+
+			client.send ResponseTypes::OK, user.to_json
 		end
 	end
 end
diff --git a/src/passwd.cr b/src/passwd.cr
index 42c241c..6811d60 100644
--- a/src/passwd.cr
+++ b/src/passwd.cr
@@ -48,6 +48,14 @@ class Passwd
 		end
 	end
 
+	def user_exists?(login : String) : Bool
+		each_user do |user|
+			return true if user.login == login
+		end
+
+		false
+	end
+
 	def get_user(uid : Int32) : AuthD::User?
 		each_user do |user|
 			if user.uid == uid
@@ -150,6 +158,10 @@ class Passwd
 		File.write(@passwd, user.to_csv + "\n", mode: "a")
 
 		add_group login, gid: gid, users: [user.login]
+
+		set_user_groups user
+
+		user
 	end
 
 	def add_group(name, password_hash = "x", gid = nil, users = Array(String).new)