Reinstate CPR using system library.

vendor/CPR/include/cpr/auth.h

@@ -0,0 +1,31 @@
+#ifndef CPR_AUTH_H
+#define CPR_AUTH_H
+
+#include <string>
+
+#include <utility>
+
+namespace cpr {
+
+class Authentication {
+  public:
+    Authentication(const std::string& username, const std::string& password)
+            : auth_string_{username + ":" + password} {}
+    Authentication(std::string&& username, std::string&& password)
+            : auth_string_{std::move(username) + ":" + std::move(password)} {}
+    Authentication(const Authentication& other) = default;
+    Authentication(Authentication&& old) noexcept = default;
+    virtual ~Authentication() noexcept = default;
+
+    Authentication& operator=(Authentication&& old) noexcept = default;
+    Authentication& operator=(const Authentication& other) = default;
+
+    virtual const char* GetAuthString() const noexcept;
+
+  protected:
+    std::string auth_string_;
+};
+
+} // namespace cpr
+
+#endif