ServiceNow REST API enables you to access Instance resources. You can create, read, update, and delete records on your ServiceNow instance after registering your application and getting authentication tokens for a user or resource.

To create the ServiceNow API Client ID and Client Secret, follow the steps listed in this article.

(Example Application Registration)

ServiceNow authentication validates the identity of a user who accesses an instance and then authorizes the user to features that match the user’s role or job function. You can use several different methods to authenticate users. We are using the password grant type approach here.

The ServiceNow Table API allows you to perform operations on existing tables.

Servicenow recommends exporting data in chunks in case of extensive data set with millions of records to avoid any performance implications and impact on other services running on the system. The Aggregate API allows you to get statistics about the existing table and retrieve records by using the pagination technique.

Sample Script

This sample script shows how to pull data from ServiceNow Table and print the table details in the console window.

# ServiceNow Instance Configuration
$servicenowInstance = @{
    Name            = "your_instance_name" # ServiceNow Instance Name
    APIVersion      = "api/now/v1" # ServiceNow API Version
    ClientID        = $env:ServiceNowClientID # To be set in the environment
    ClientSecret    = $env:ServiceNowClientSecret # To be set in the environment
    Username        = $env:ServiceNowUsername # To be set in the environment
    Password        = $env:ServiceNowPassword # To be set in the environment
    ItemsPerAPICall = 100 # Number of items to be retrieved in a single API call
}

# Get Acccess Token from ServiceNow
Function GetAccessToken () {
    try {
        Write-Host "Getting Access Token" -ForegroundColor Green 
    
        $headers = @{
            "Content-Type" = "application/x-www-form-urlencoded"
            "Accept"       = "application/json"
        }

        $body = @{
            grant_type    = "password"
            username      = $servicenowInstance.Username 
            password      = $servicenowInstance.Password
            client_id     = $servicenowInstance.ClientID
            client_secret = $servicenowInstance.ClientSecret
        }
    
        $tokenEndpoint = "https://$($servicenowInstance.Name).service-now.com/oauth_token.do"
        $response = Invoke-RestMethod -Uri $tokenEndpoint -Method Post -Headers $headers -Body $body

        if ($response.access_token) {
            $accessToken = $response.access_token
            Write-Host "Here is the Access Token" -ForegroundColor Green
            Write-Host "$accessToken" -ForegroundColor Green -BackgroundColor Green
            return $accessToken
        }
        else {
            Write-Host "There is a problem in getting Access Token. Error: $($response.status) - $($response.error_description)" -ForegroundColor Red
            return $null
        }
    }
    catch {
        throw "There is a problem in getting Access Token. Error: $($_.Exception.Message)"
    }
}

# Get Table Data from ServiceNow
Function GetTableData () {
    [CmdletBinding()]
    param (
        [Parameter()][string]$AccessToken, [Parameter()][string]$TableName, [Parameter()][string]$Query
    )
    try {
        Write-Host "Getting $($TableName) Table Data" -ForegroundColor Green

        $headers = @{
            "Accept"        = "application/json"
            "Authorization" = "Bearer $($AccessToken)"
        }

        $statsEndpoint = "https://$($servicenowInstance.Name).service-now.com/$($servicenowInstance.APIVersion)/stats/$($TableName)?sysparm_query=$($Query)&sysparm_count=true"
        $response = Invoke-RestMethod -Uri $statsEndpoint -Method Get -Headers $headers
        [int]$numberOfRecords = $($response.result.stats.count)
        Write-Host "Number of Records found in $($TableName): $($numberOfRecords)" -ForegroundColor Green
        $iterations = [Math]::Ceiling($numberOfRecords / $($servicenowInstance.ItemsPerAPICall))
        Write-Host "Number of iterations required to get all the records from this table : $($iterations)" -ForegroundColor Green

        $tableData = $null

        for ($i = 0; $i -lt $iterations; $i++) {
            $offset = $($i * $($servicenowInstance.ItemsPerAPICall))
            $query = "$($Query)&sysparm_display_value=all&sysparm_limit=$($servicenowInstance.ItemsPerAPICall)&sysparm_offset=$($offset)"
            $tableDataEndpoint = "https://$($servicenowInstance.Name).service-now.com/$($servicenowInstance.APIVersion)/table/$($TableName)?sysparm_query=$($query)"
            $response = Invoke-RestMethod -Uri $tableDataEndpoint -Method Get -Headers $headers
            $tableData += $($response.result)
        }

        return $tableData
    }
    catch {
        Write-Host "There is a problem in getting $($TableName) Table Data. Error: $($_.Exception.Message)" -ForegroundColor Red
    }
}

# Print Table Data
Function PrintTableData () {
    
    param (
        $TableData
    )

    foreach ($record in $TableData) {
        $recordNumber = $record.number.display_value
        $recordSysId = $record.sys_id.display_value
        $first3CharsOfNumber = [string]$recordNumber.SubString(0, 3)
        
        switch ($first3CharsOfNumber) {
            "CHG" { $tableName = "change_request"; break }  
            "INC" { $tableName = "incident"; break }
            "TAS" { $tableName = "sc_task"; break }
            default { $tableName = $null; break }
        }

        if ($tableName) {
            $recordLink = "https://$($servicenowInstance.Name).service-now.com/nav_to.do?uri=$($tableName).do?sys_id=$($recordSysId)"
            Write-Host "Record Number: $($recordNumber) - Record Link: $($recordLink)" -ForegroundColor Green
        }
        else {
            Write-Host "Unable to create Record Link for $($recordNumber)" -ForegroundColor Red
        }
    }
}

# ****** Main Script Starts ******

try {
    $accessToken = GetAccessToken

    if ($accessToken) {
        $executionTime = [DateTime]::Now
        $oneYearBefore = $executionTime.AddYears(-1).ToString("yyyy-MM-dd HH:mm:ss")
        $tableData = GetTableData -AccessToken $accessToken -TableName "incident" -Query "sys_created_on>=$($oneYearBefore)^assigned_to=^ORDERBYsys_created_on"
        
        if ($tableData.Count -gt 0) {
            PrintTableData -TableData $tableData
            Write-Host "Successfully got the data" -ForegroundColor Green
        }
        else {
            Write-Host "There is no data in the table" -ForegroundColor Yellow
        }
    }
    else {
        Write-Host "Access Token is empty/null" -ForegroundColor Red
    }
}
catch {
    Write-Host "There is a problem in running this script. Error: $($_.Exception.Message)" -ForegroundColor Red    
}

# ****** Main Script Ends ******

Sample Script Execution Output