service/pam: move pam execution to subprocess to allow killing it

Many pam modules can't be aborted well without this.

src/services/pam/ipc.hpp

@@ -0,0 +1,43 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+#include <string>
+
+#include <qtclasshelpermacros.h>
+
+enum class PamIpcEvent : uint8_t {
+	Request,
+	Exit,
+};
+
+enum class PamIpcExitCode : uint8_t {
+	Success,
+	StartFailed,
+	AuthFailed,
+	MaxTries,
+	PamError,
+	OtherError,
+};
+
+struct PamIpcRequestFlags {
+	bool echo;
+	bool error;
+	bool responseRequired;
+};
+
+class PamIpcPipes {
+public:
+	explicit PamIpcPipes() = default;
+	explicit PamIpcPipes(int fdIn, int fdOut): fdIn(fdIn), fdOut(fdOut) {}
+	~PamIpcPipes();
+	Q_DISABLE_COPY_MOVE(PamIpcPipes);
+
+	[[nodiscard]] bool readBytes(char* buffer, size_t length) const;
+	[[nodiscard]] bool writeBytes(const char* buffer, size_t length) const;
+	[[nodiscard]] std::string readString(bool* ok) const;
+	[[nodiscard]] bool writeString(const std::string& string) const;
+
+	int fdIn = 0;
+	int fdOut = 0;
+};