fix(sign): sign the raw path

[koho]

For now, we only sign the filename and timestamp to generate a download link. But this may cause a security problem that someone can bypass authentication to access file in other protected storage.

For example, we have two local storages protected with different password:

• /s1
  • f1.txt
• /s2
  • f1.txt

The two files that have the same names (content may differ) but in different storages. Let /s1 be the root directory of user u1 and copy the download link of f1.txt. The link is working with a suffix /d/s1/f1.txt?sign=xxxxx. Now we change s1 to s2 in the link, the file f1.txt in s2 is successfully downloaded.

If we sign the whole file path, we can identify this path hack as invalid signature.

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