feat: add additional supported interfaces

This includes the relevant auth headers and a simplification of several others.

src/util/AsyncHandler.ts

@@ -0,0 +1,17 @@
+/**
+ * Simple interface for classes that can potentially handle a specific kind of data asynchronously.
+ */
+export interface AsyncHandler<TInput, TOutput = void> {
+  /**
+   * Checks if the input data can be handled by this class.
+   * @param input - Input data that would be handled potentially.
+   * @returns A promise resolving to if this input can be handled.
+   */
+  canHandle: (input: TInput) => Promise<boolean>;
+  /**
+   * Handles the given input. This should only be done if the {@link canHandle} function returned `true`.
+   * @param input - Input data that needs to be handled.
+   * @returns A promise resolving when the handling is finished. Return value depends on the given type.
+   */
+  handle: (input: TInput) => Promise<TOutput>;
+}