This change replaces the non-constant time comparison of
request signatures with a constant time implementation. This
prevents a timing attack which can be used to learn a valid
signature for a request without knowing the secret key.
Fixes#5334
This change introduces following simplified steps to follow
during config migration.
```
// Steps to move from version N to version N+1
// 1. Add new struct serverConfigVN+1 in config-versions.go
// 2. Set configCurrentVersion to "N+1"
// 3. Set serverConfigCurrent to serverConfigVN+1
// 4. Add new migration function (ex. func migrateVNToVN+1()) in config-migrate.go
// 5. Call migrateVNToVN+1() from migrateConfig() in config-migrate.go
// 6. Make changes in config-current_test.go for any test change
```
Verify() was being called by caller after the data
has been successfully read after io.EOF. This disconnection
opens a race under concurrent access to such an object.
Verification is not necessary outside of Read() call,
we can simply just do checksum verification right inside
Read() call at io.EOF.
This approach simplifies the usage.
Content-Encoding is set to "aws-chunked" which is an S3 specific
API value which is no meaning for an object. This is how S3
behaves as well for a streaming signature uploaded object.
* Refactor streaming signatureV4 w/ state machine
- Used state machine to make transitions between reading chunk header,
chunk data and trailer explicit.
* debug: add print/panic statements to gather more info on CI failure
* Persist lastChunk status between Read() on ChunkReader
... remove panic() which was added as interim aid for debugging.
* Add unit-tests to cover v4 streaming signature
