diff --git a/src/main-ipc.cr b/src/main-ipc.cr
new file mode 100644
index 0000000..797d357
--- /dev/null
+++ b/src/main-ipc.cr
@@ -0,0 +1,117 @@
+require "uuid"
+require "option_parser"
+
+require "ipc"
+require "jwt"
+
+require "pg"
+require "crecto"
+
+require "./user.cr"
+
+authd_db_name = "authd"
+authd_db_hostname = "localhost"
+authd_db_user = "user"
+authd_db_password = "nico-nico-nii"
+authd_jwt_key = "nico-nico-nii"
+
+OptionParser.parse! do |parser|
+	parser.on "-d name", "--database-name name", "Database name." do |name|
+		authd_db_name = name
+	end
+
+	parser.on "-u name", "--database-username user", "Database user." do |name|
+		authd_db_user = name
+	end
+
+	parser.on "-a host", "--hostname host", "Database host name." do |host|
+		authd_db_hostname = host
+	end
+
+	parser.on "-P file", "--password-file file", "Password file." do |file_name|
+		authd_db_password = File.read(file_name).chomp
+	end
+
+	parser.on "-K file", "--key-file file", "JWT key file" do |file_name|
+		authd_jwt_key = File.read(file_name).chomp
+	end
+end
+
+class AuthD::Message
+	enum RequestTypes
+		TOKEN_REQUEST
+	end
+	enum ResponseTypes
+		ALL_OK
+		INVALID_FORMAT
+		INVALID_CREDENTIALS
+	end
+
+	JSON.mapping({
+		username: String,
+		password: String,
+	})
+end
+
+module DataBase
+	extend Crecto::Repo
+end
+
+DataBase.config do |conf|
+	conf.adapter = Crecto::Adapters::Postgres
+	conf.hostname = authd_db_hostname
+	conf.database = authd_db_name
+	conf.username = authd_db_user
+	conf.password = authd_db_password
+end
+
+# Dummy query to check DB connection is possible.
+begin
+	DataBase.all AuthD::User, Crecto::Repo::Query.new
+rescue e
+	puts "Database connection failed: #{e.message}"
+
+	exit 0
+end
+
+authd = IPC::Service.new("authd").loop do |event|
+	p event.class
+	if event.is_a? IPC::Event::Message
+		payload = JSON.parse(event.message.payload).as_h?
+
+		if payload.nil?
+			event.client.send AuthD::Message::ResponseTypes::INVALID_FORMAT.to_u8, "Input is not a JSON object."
+			next
+		end
+
+		username = payload["username"]?.try &.as_s?
+		password = payload["password"]?.try &.as_s?
+
+		if username.nil?
+			event.client.send AuthD::Message::ResponseTypes::INVALID_FORMAT.to_u8, "Missing username."
+			next
+		end
+
+		if password.nil?
+			event.client.send AuthD::Message::ResponseTypes::INVALID_FORMAT.to_u8, "Missing password."
+			next
+		end
+
+		# FIXME: Huge pitfall here. Somehow doesn’t compile without, but that should be its type already, so…?
+		username = username.as String
+		password = password.as String
+
+		user = DataBase.get_by AuthD::User, username: username, password: password
+
+		if user.nil?
+			event.client.send AuthD::Message::ResponseTypes::INVALID_CREDENTIALS.to_u8, "Invalid credentials.."
+
+			next
+		end
+
+		event.client.send AuthD::Message::ResponseTypes::ALL_OK.to_u8, JWT.encode(user.to_h, authd_jwt_key, "HS255")
+	end
+end
+
+authd.close # Not exactly required because an at_exit{} is added, but…
+