Add signed encryption scope field to string-to-sign for authorization for SAS

[psolymos]

Helo, I have encountered an issue with SAS and this PR represents a fix referencing Azure SAS spec changes:

1. https://learn.microsoft.com/en-us/rest/api/storageservices/create-user-delegation-sas#version-2020-12-06-and-later
2. https://learn.microsoft.com/en-us/rest/api/storageservices/create-service-sas#version-2020-12-06-and-later (actually the docs are also wrong there omitting the rsct field)

Here is how the user delegation SAS fields lined up:

spec	pkg
signedPermissions	permissions
signedStart	dates$start
signedExpiry	dates$expiry
canonicalizedResource	resource
signedKeyObjectId	key$SignedOid
signedKeyTenantId	key$SignedTid
signedKeyStart	key$SignedStart
signedKeyExpiry	key$SignedExpiry
signedKeyService	key$SignedService
signedKeyVersion	key$SignedVersion
signedAuthorizedUserObjectId
signedUnauthorizedUserObjectId
signedCorrelationId
signedIP	ip
signedProtocol	protocol
signedVersion	auth_api_version
signedResource	resource_type
signedSnapshotTime	snapshot_time
signedEncryptionScope	MISSING
rscc
rscd
rsce
rscl
rsct

Because of this, I was getting Signature did not match. String to sign used was ... error. Installing from my fork resolved the issue.

Cheers!

[hongooi73]

Hmm, I don't recall running into problems with SAS, but this was some time ago

[psolymos]

@hongooi73 any plans for merging this for a new CRAN release? Thanks.

[sam-bradshaw-wcmc]

I have also encountered problems with the SAS tokens generated by this library (with a similar error message), and it looks like I'm not the only one https://github.com/Azure/AzureStor/issues/140

This post was actually very helpful for me to help work around the issue. If I set auth_api_version="2020-10-02" the SAS token generated start working. The API version needs to be one before 2020-12-06 in which this breaking change seems to have occurred