Scope
- Access to private Azure Blob Storage requires authentication.
- Shared Key authentication represents one of the authentication options.
Example
Download: azure_authentication_shared_key_sample.ps1
# inspired by:
# https://stackoverflow.com/questions/53653473/generating-an-sas-token-in-java-to-download-a-file-in-an-azure-data-storage-cont?rq=1
# https://purple.telstra.com.au/blog/loading-and-querying-data-in-azure-table-storage-using-powershell
# https://docs.microsoft.com/en-us/rest/api/storageservices/authorize-with-shared-key
function Create-Signature( [string] $Operation, [string] $Container, [string] $Blob, [string] $Account, [string] $AccessKey, [string] $Version, [DateTime] $Now, [int] $ContentLength=-1 )
{
[Reflection.Assembly]::LoadWithPartialName("System.Web") | Out-Null
$partToSign = "`n" `
+ "`n" `
+ "`n" `
+ (($ContentLength -gt -1) ? $ContentLength : '') + "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "x-ms-blob-type:BlockBlob" + "`n" `
+ "x-ms-date:$(Get-Date (Get-Date $Now).ToUniversalTime() -Format 'R')" + "`n" `
+ "x-ms-version:$Version" + "`n"
switch ( $Operation )
{
'GET' {
$stringToSign = 'GET' `
+ $partToSign `
+ "/$Account/$Container/$Blob"
break
}
'PUT' {
$stringToSign = 'PUT' `
+ $partToSign `
+ "/$Account/$Container/$Blob"
break
}
'LIST' {
$stringToSign = "GET" `
+ $partToSign `
+ "/$Account/$Container" + "`n" `
+ "comp:list" + "`n" `
+ "restype:container"
break
}
default {
throw "invalid operation: $Operation"
}
}
$hmac = New-Object System.Security.Cryptography.HMACSHA256
$hmac.key = [Convert]::FromBase64String( $AccessKey )
$signature = $hmac.ComputeHash( [Text.Encoding]::UTF8.GetBytes( $stringToSign ) )
$signature = [Convert]::ToBase64String( $signature )
Write-Debug "container: $Container"
Write-Debug "Accoount: $Account"
Write-Debug "AccessKey: $AccessKey"
Write-Debug "stringToSign: $stringToSign"
$signature
}
function Invoke-BlobRequest( [Uri] $Uri, [string] $Account, [string] $Signature, [DateTime] $Now, [string] $Version, [string] $Method='GET', [string] $FilePath='' )
{
$requestParams = @{}
$requestParams.Add( 'Uri', $Uri )
$requestParams.Add( 'Method', $Method )
if ( $FilePath )
{
$requestParams.Add( 'Infile', $FilePath )
}
$requestParams.Add( 'Headers', @{ `
'x-ms-blob-type' = 'BlockBlob'; `
'x-ms-date' = "$(Get-Date (Get-Date $Now).ToUniversalTime() -Format 'R')"; `
'x-ms-version' = $Version; `
'Authorization' = "SharedKey $($Account):$($Signature)" `
} `
)
Write-Debug ".... Invoke-WebRequest: $Uri"
$requestParams.Keys | % {
if ( $_ -eq 'Headers' )
{
$item = $_
$requestParams.Item($_).Keys | % {
Write-Debug "...... Headers $_ : $($requestParams.Item($item).Item($_))"
}
} else {
Write-Debug "...... $_ $($requestParams.Item($_))"
}
}
# run the web service request
$response = Invoke-WebRequest @requestParams
$response
}
# ---------- ---------- ----------
# Main
# ---------- ---------- ----------
$ownerAccount = '<storage account>'
$ownerAccessKey = '<storage account access key>'
$requesterAccount = '<requester account>'
$version = '2019-10-10'
# consider badly synchronized server time and start 3 minutes in the past
$now = (Get-Date).ToUniversalTime().AddMinutes(-3)
Write-Host "`n"
Write-Host "# ++++++++++++++++++++++++++++++"
Write-Host "# List Blobs in Container"
Write-Host "# ++++++++++++++++++++++++++++++"
# step 1: create signature
$container = 'yade'
$signature = Create-Signature -Operation 'LIST' -Container $container -Account $ownerAccount -AccessKey $ownerAccessKey -Version $version -Now $now
Write-Debug "Signature: $signature"
# step 2: send web service request
$uri = "https://$($ownerAccount).blob.core.windows.net/$($container)?restype=container&comp=list"
$response = Invoke-BlobRequest -Uri $uri -Account $requesterAccount -Signature $signature -Now $now -Version $version -Method 'GET'
Write-Host "Status Code: $($response.StatusCode)"
Write-Host $response.Content
Write-Host "`n"
Write-Host "# ++++++++++++++++++++++++++++++"
Write-Host "# Get Blob from Container"
Write-Host "# ++++++++++++++++++++++++++++++"
# step 1: create signature
$container = 'yade'
$blob = 'test.txt'
$signature = Create-Signature -Operation 'GET' -Container $container -Blob $blob -Account $ownerAccount -AccessKey $ownerAccessKey -Version $version -Now $now
Write-Debug "Signature: $signature"
# step 2: send web service request
$uri = "https://$($ownerAccount).blob.core.windows.net/$($container)/$($blob)"
$response = Invoke-BlobRequest -Uri $uri -Account $requesterAccount -Signature $signature -Now $now -Version $version -Method 'GET'
Write-Host "Status Code: $($response.StatusCode)"
Write-Host $response.Content
Write-Host "`n"
Write-Host "# ++++++++++++++++++++++++++++++"
Write-Host "# Write Blob to Container"
Write-Host "# ++++++++++++++++++++++++++++++"
# step 1: create signature
$container = 'yade'
$filePath = "c:/tmp/some_blob.txt"
$blob = (Get-Item $filePath).Name
$signature = Create-Signature -Operation 'PUT' -Container $container -Blob $blob -Account $ownerAccount -AccessKey $ownerAccessKey -Version $version -Now $now -ContentLength (Get-Content $filePath -Raw).length
Write-Debug "Signature: $signature"
# step 2: send web service request
$uri = "https://$($ownerAccount).blob.core.windows.net/$($container)/$($blob)"
$response = Invoke-BlobRequest -Uri $uri -Account $requesterAccount -Signature $signature -Now $now -Version $version -Method 'PUT' -FilePath $filePath
Write-Host "Status Code: $($response.StatusCode)"
Write-Host $response.Content
Explanations
The Shared Key authentication enable unlimited access i.e it does not have any expiry. Refer to the Azure article Authorize with Shared Key for reference. The above PowerShell script creates the Shared Key for three operation LIST, GET, PUT. The three operation support three different process:
- LIST BLOB
- The LIST BLOB operation displays the list of blobs in the container.
- GET BLOB
- The GET BLOB operation is used to get the content in a blob.
- PUT BLOB
- The PUT BLOB operation is used to create a blob and adding a content to it or writing to a blob.
The Shared Key uses different parameters for different operation. The Shared Key requires a String which is to be encoded and need to passed as a Authorization Header in the request.
The format for signature string is:
StringToSign = VERB + "\n" +
Content-Encoding + "\n" +
Content-Language + "\n" +
Content-Length + "\n" +
Content-MD5 + "\n" +
Content-Type + "\n" +
Date + "\n" +
If-Modified-Since + "\n" +
If-Match + "\n" +
If-None-Match + "\n" +
If-Unmodified-Since + "\n" +
Range + "\n" +
CanonicalizedHeaders +
CanonicalizedResource;
The StringToSIgn is then encoded using HMAC-SHA256 algorithm over the UTF-8-encoded signature string which is then used as an Authorization Header using syntax:
Authorization="SharedKey <AccountName>:<Signature>"
where SharedKey is the authorization scheme, Account name is the name of account by which request is generated, Signature is the encoded StringToSign
Signature String
The StringToSign parameters differ according to the operations:
LIST BLOB:
In the LIST BLOB operation lists the blobs in the container. The StringToSign for LIST BLOB will be:
$stringToSign = "GET" `
+ "`n" `
+ "`n" `
+ "`n" `
+ (($ContentLength -gt -1) ? $ContentLength : '') + "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "x-ms-blob-type:BlockBlob" + "`n" `
+ "x-ms-date:$(Get-Date (Get-Date $Now).ToUniversalTime() -Format 'R')" + "`n" `
+ "x-ms-version:$Version" + "`n" `
+ "/$Account/$Container" + "`n" `
+ "comp:list" + "`n" `
+ "restype:container"
where $Account is the account by which request is generated. $Container is the name of the container.
GET BLOB:
The GTE BLOB operation displays the content of the blob. So, for the get operation it is required to pass the blob name whose content is to be read/get. So, the StringToSign for GET BLOB will be:
$stringToSign = 'GET' `
+ "`n" `
+ "`n" `
+ "`n" `
+ (($ContentLength -gt -1) ? $ContentLength : '') + "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "x-ms-blob-type:BlockBlob" + "`n" `
+ "x-ms-date:$(Get-Date (Get-Date $Now).ToUniversalTime() -Format 'R')" + "`n" `
+ "x-ms-version:$Version" + "`n" `
+ "/$Account/$Container/$Blob"
where $Account is the account by which request is generated. $Container is the name of the container. $Blob is the name of the blob whose content is to be Get.
PUT BLOB
The PUT BLOB operation creates a new block or updates an existing block blob. The PUT BLOB creates a BLOB of a length of content in a file so it is required to pass the length of the blob so that it can allocate a that much memory in the Container and can write the file content to the blob. The StringToSign for the PUT BLOB will be:
$stringToSign = 'PUT' `
+ "`n" `
+ "`n" `
+ "`n" `
+ (($ContentLength -gt -1) ? $ContentLength : '') + "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "`n" `
+ "x-ms-blob-type:BlockBlob" + "`n" `
+ "x-ms-date:$(Get-Date (Get-Date $Now).ToUniversalTime() -Format 'R')" + "`n" `
+ "x-ms-version:$Version" + "`n" `
+ "/$Account/$Container/$Blob"
where $Account is the account by which request is generated. $Container is the name of the container. $Blob is the name of the blob which is to be created. The $ContentLength for the LIST BLOB and GET BLOB operation will be empty but for the PUT BLOB it required to pass the Content Length for the file to be created.
Encoding Signature String
After creating Signature string it is required to encode the string to create a Shared Key which can then be passed to the Authorization header. The algorithm used for encoding is HMAC-SHA256 over the UTF-8-encoded signature string. The script used in PowerShell to encode the StringToSign is:
$hmac = New-Object System.Security.Cryptography.HMACSHA256
$hmac.key = [Convert]::FromBase64String( $AccessKey )
$signature = $hmac.ComputeHash( [Text.Encoding]::UTF8.GetBytes( $stringToSign ) )
$signature = [Convert]::ToBase64String( $signature )
where $AccessKey is the access key for the Azure blob container. $stringToSign is the signature string which depends on the type of operation.
Request to Azure
The request to the azure is used to invoke the call. This takes different types of URI for different operations. The URI depends on the type of operation we want to use in the request. The header used in the requests are:
'x-ms-blob-type' = 'BlockBlob'; `
'x-ms-date' = "$(Get-Date (Get-Date $Now).ToUniversalTime() -Format 'R')"; `
'x-ms-version' = $Version; `
'Authorization' = "SharedKey $($Account):$($Signature)" `
where header
The details about the type of request in the operations are:
LIST BLOB
The request URI for the LIST BLOB just includes the container name. As the LIST operations lists all the blobs in the container. So the request URI will be https://$($ownerAccount).blob.core.windows.net/$($container)?restype=container&comp=list where $ownerAccount is the name of the Account and $container is the name of the container.
The request and header syntax for LIST BLOB will be:
Request Syntax
GET https://$($ownerAccount).blob.core.windows.net/$($container)?restype=container&comp=list
Request Headers
x-ms-blob-type: BlockBlob
x-ms-date: <date>
x-ms-version: $Version
Authorization="SharedKey <AccountName>:<Signature>"
GET BLOB
The GET BLOB is used to read the blob content so it is required to pass the blob name in the URI. So the request URI for the GET BLOB will be https://$($ownerAccount).blob.core.windows.net/$($container)/$($blob) where $ownerAccount is the name of the Account and $container is the name of the container and $blob is the name of the blob which is to be read.The request and header syntax for GET BLOB will be:
Request Syntax
GET https://$($ownerAccount).blob.core.windows.net/$($container)/$($blob)
Request Headers
x-ms-blob-type: BlockBlob
x-ms-date: <date>
x-ms-version: $Version
Authorization="SharedKey <AccountName>:<Signature>"
PUT BLOB
The PUT BLOB operation is used to create a blob. So the URI for the PUT BLOB includes the name of the blob to be created and the content of the blob is to be passed in request body. The URI will be https://$($ownerAccount).blob.core.windows.net/$($container)/$($blob) where $ownerAccount is the name of the Account and $container is the name of the container and $blob is the name of the blob which is to be created in the container.
Request Syntax
PUT https://$($ownerAccount).blob.core.windows.net/$($container)/$($blob)
Request Headers
x-ms-blob-type: BlockBlob
x-ms-date: <date>
x-ms-version: $Version
Authorization="SharedKey <AccountName>:<Signature>"
Request Body:
<Content of the File>