Sends an HTTP or HTTPS request to a SharePoint Online REST-compliant web service using Windows PowerShell.

Custom Windows PowerShell Function to Make SharePoint REST Service Calls

The functions in this Gist are part of an article series on ITUnity.com.

Clear-SPORestCredentials.ps1

<#
.Synopsis
    Clears the SharePoint Online credentials stored in the global variable.
.DESCRIPTION
    Clears the SharePoint Online credentials stored in the global variable.
    You can also manually clear the variable by explicitly setting 
    $global:spoCred = $null.
.EXAMPLE
   Clear-SPORestCredentials
#>
function global:Clear-SPORestCredentials {
    $global:spoCred = $null
}

Invoke-SPORestMethod.ps1

<#
.Synopsis
    Sends an HTTP or HTTPS request to a SharePoint Online REST-compliant web service.
.DESCRIPTION
    This function sends an HTTP or HTTPS request to a Representational State 
    Transfer (REST)-compliant ("RESTful") SharePoint Online web service.
    When connecting, if Set-SPORestCredentials is not called then you will be
    prompted for your credentials. Those credentials are stored in a global
    variable $global:spoCred so that it will be available on subsequent calls.
    Call Clear-SPORestCredentials to clear the variable.
.EXAMPLE
   Invoke-SPORestMethod -Url "https://contoso.sharepoint.com/_api/web"
.EXAMPLE
   Invoke-SPORestMethod -Url "https://contoso.sharepoint.com/_api/contextinfo" -Method "Post"
#>
function global:Invoke-SPORestMethod {
    [CmdletBinding()]
    [OutputType([int])]
    Param (
        # The REST endpoint URL to call.
        [Parameter(Mandatory = $true, ValueFromPipeline = $true, Position = 0)]
        [ValidateNotNullOrEmpty()]
        [System.Uri]$Url,

        # Specifies the method used for the web request. The default value is "Get".
        [Parameter(Mandatory = $false, Position = 1)]
        [ValidateNotNullOrEmpty()]
        [ValidateSet("Get", "Head", "Post", "Put", "Delete", "Trace", "Options", "Merge", "Patch")]
        [string]$Method = "Get",

        # Additional metadata that should be provided as part of the Body of the request.
        [Parameter(Mandatory = $false, Position = 2)]
        [ValidateNotNullOrEmpty()]
        [object]$Metadata,

        # The "X-RequestDigest" header to set. This is most commonly used to provide the form digest variable. Use "(Invoke-SPORestMethod -Url "https://contoso.sharepoint.com/_api/contextinfo" -Method "Post").GetContextWebInformation.FormDigestValue" to get the Form Digest value.
        [Parameter(Mandatory = $false, Position = 3)]
        [ValidateNotNullOrEmpty()]
        [string]$RequestDigest,
        
        # The "If-Match" header to set. Provide this to make sure you are not overwritting an item that has changed since you retrieved it.
        [Parameter(Mandatory = $false, Position = 4)]
        [ValidateNotNullOrEmpty()]
        [string]$ETag, 
        
        # To work around the fact that many firewalls and other network intermediaries block HTTP verbs other than GET and POST, specify PUT, DELETE, or MERGE requests for -XHTTPMethod with a POST value for -Method.
        [Parameter(Mandatory = $false, Position = 5)]
        [ValidateNotNullOrEmpty()]
        [ValidateSet("Get", "Head", "Post", "Put", "Delete", "Trace", "Options", "Merge", "Patch")]
        [string]$XHTTPMethod,

        [Parameter(Mandatory = $false, Position = 6)]
        [ValidateNotNullOrEmpty()]
        [ValidateSet("Verbose", "MinimalMetadata", "NoMetadata")]
        [string]$JSONVerbosity = "Verbose",

        # If the returned data is a binary data object such as a file from a SharePoint site specify the output file name to save the data to.
        [Parameter(Mandatory = $false, Position = 7)]
        [ValidateNotNullOrEmpty()]
        [string]$OutFile
    )

    Begin {
        if ((Get-Module Microsoft.Online.SharePoint.PowerShell -ListAvailable) -eq $null) {
            throw "The Microsoft SharePoint Online PowerShell cmdlets have not been installed."
        }
        if ($global:spoCred -eq $null) {
            [System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Client.Runtime") | Out-Null
            $cred = Get-Credential -Message "Enter your credentials for SharePoint Online:"
            $global:spoCred = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($cred.UserName, $cred.Password)
        } 

    }
    Process {
        $request = [System.Net.WebRequest]::Create($Url)
        $request.Credentials = $global:spoCred
        $odata = ";odata=$($JSONVerbosity.ToLower())"
        $request.Accept = "application/json$odata"
        $request.ContentType = "application/json$odata"   
        $request.Headers.Add("X-FORMS_BASED_AUTH_ACCEPTED", "f")   
        $request.Method = $Method.ToUpper()

        if(![string]::IsNullOrEmpty($RequestDigest)) {
            $request.Headers.Add("X-RequestDigest", $RequestDigest)
        }
        if(![string]::IsNullOrEmpty($ETag)) {
            $request.Headers.Add("If-Match", $ETag)
        }
        if($XHTTPMethod -ne $null) {
            $request.Headers.Add("X-HTTP-Method", $XHTTPMethod.ToUpper())
        }
        if ($Metadata -is [string] -and ![string]::IsNullOrEmpty($Metadata)) {
            $body = [System.Text.Encoding]::UTF8.GetBytes($Metadata)
            $request.ContentLength = $body.Length
            $stream = $request.GetRequestStream()
            $stream.Write($body, 0, $body.Length)
        } elseif ($Metadata -is [byte[]] -and $Metadata.Count -gt 0) {
            $request.ContentLength = $Metadata.Length
            $stream = $request.GetRequestStream()
            $stream.Write($Metadata, 0, $Metadata.Length)
        } else {
            $request.ContentLength = 0
        }
 

        $response = $request.GetResponse()
        try {
            $streamReader = New-Object System.IO.StreamReader $response.GetResponseStream()
            try {
                # If the response is a file (a binary stream) then save the file our output as-is.
                if ($response.ContentType.Contains("application/octet-stream")) {
                    if (![string]::IsNullOrEmpty($OutFile)) {
                        $fs = [System.IO.File]::Create($OutFile)
                        try {
                            $streamReader.BaseStream.CopyTo($fs)
                        } finally {
                            $fs.Dispose()
                        }
                        return
                    }
                    $memStream = New-Object System.IO.MemoryStream
                    try {
                        $streamReader.BaseStream.CopyTo($memStream)
                        Write-Output $memStream.ToArray()
                    } finally {
                        $memStream.Dispose()
                    }
                    return
                }
                # We don't have a file so assume JSON data.
                $data = $streamReader.ReadToEnd()

                # In many cases we might get two ID properties with different casing.
                # While this is legal in C# and JSON it is not with PowerShell so the
                # duplicate ID value must be renamed before we convert to a PSCustomObject.
                if ($data.Contains("`"ID`":") -and $data.Contains("`"Id`":")) {
                    $data = $data.Replace("`"ID`":", "`"ID-dup`":");
                }

                $results = ConvertFrom-Json -InputObject $data

                # The JSON verbosity setting changes the structure of the object returned.
                if ($JSONVerbosity -ne "verbose" -or $results.d -eq $null) {
                    Write-Output $results
                } else {
                    Write-Output $results.d 
                }
            } finally {
                $streamReader.Dispose()
            }
        } finally {
            $response.Dispose()
        }
    }
    End {
    }
} 

Set-SPORestCredentials.ps1

<#
.Synopsis
    Stores the credentials for Invoke-SPORestMethod.
.DESCRIPTION
    Stores the credentials for Invoke-SPORestMethod. This is done so that you
    don't have to provide your credentials on every call to Invoke-SPORestMethod.
.EXAMPLE
   Set-SPORestCredentials
.EXAMPLE
   Set-SPORestCredentials -Credential $cred
#>
function global:Set-SPORestCredentials {
    Param (
        [Parameter(ValueFromPipeline = $true)]
        [ValidateNotNull()]
        $Credential = (Get-Credential -Message "Enter your credentials for SharePoint Online:")
    )
    Begin {
        if ((Get-Module Microsoft.Online.SharePoint.PowerShell -ListAvailable) -eq $null) {
            throw "The Microsoft SharePoint Online PowerShell cmdlets have not been installed."
        }
        [System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Client.Runtime") | Out-Null
    }
    Process {
        $global:spoCred = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Credential.UserName, $Credential.Password)
    }
} 

Thanks a lot 😄
To check $spocred I used this, otherwise powerhsell throw an error variable is undefined
if ( (test-path variable:spoCred) -eq $false){ ... }