TODO

TODO:
	Official Integration Checklist:
		✔ Do not store `accountId` provided by user.
			- Only store `accountId` from API authorize response.

		✔ Set a `User-Agent` header.

		✘ Multi-threaded uploads
			- PHP isn't great at multi-threading.
		✘ Multi-threaded downloads
			- PHP isn't great at multi-threading.
		
		☐ Handle HTTP 503 errors from any call except `b2_upload_*`
			- Make another attempt.
			- May include `Retry-After` header.
			- Use exponential back-off by default.
		☐ Handle HTTP 503 errors for `b2_upload_file` and `b2_upload_part`
			- Obtain new upload URL and auth token

		☐ Handle HTTP 401 errors for all calls
			- Code `unauthorized` - don't retry
			- Code `bad_auth_token` or `expired_auth_token` - obtain new account authorization
		
		☐ Interoperability metadata
			✔ X-Bz-Info-src_last_modified_millis
			☐ X-Bz-Info-large_file_sha1
		
		✔ Deleting file versions
			- Handle deleting the latest version or all versions.
		
		✘ Timing background work
			- Not applicable
		
		✔ Creating buckets
			- Buckets are created as **private** by default
		
		☐ Re-attempt `b2_upload_file` and `b2_upload_part` and fetch new upload URL when:
			- An HTTPS connection cannot be made. (e.g., connection timeout).
			- The HTTPS connection is broken. (e.g., broken pipe or connection reset)
			- The HTTPS connection times out waiting for a response (socket timeout).
			- The HTTP response status is 408 (Request Timeout).
			- The HTTP response status is between 500-599, including 503 Service Unavailable.
	
	Tests:
		☐ Test all auxillary objects
	Integration Tests:
		☐ Send `X-Bz-Test-Mode: fail_some_uploads` header on `b2_upload_file` calls.
		☐ Send `X-Bz-Test-Mode: expire_some_account_authorization_tokens` header.
		☐ Send `X-Bz-Test-Mode: force_cap_exceeded` header on upload/download related calls.
	Objects:
		☐ CORS Rule
		☐ Lifecycle Rule
		☐ File Retention
		☐ SSE