Using Wordpress API's with PowerShell. Associated blogpost https://blog.darrenjrobinson.com/using-wordpress-apis-with-powershell/

WordPress API Authentication.ps1

# V2 APIs
# Basic AuthN

$userID = 'yourWordpressAccountAlias'
$userPassword = 'ABCD wTUZ pIST 9jEo 99LV 1234'
$Bytes = [System.Text.Encoding]::utf8.GetBytes("$($userID):$($userPassword)")
$encodedAuth = [Convert]::ToBase64String($Bytes)
$header = @{Authorization = "Basic $($encodedAuth)" }

Invoke-RestMethod -method get -uri "https://yourwordpressURL/wp-json/wp/v2/posts" -headers $header

# ===================================================================================================


# V1 APIs
<#

Update the following snippet with the clientID from your newly registered WordPress application and the URL from your WordPress site. 
It must be the same as you registered with the application registration. 
Running the snippet below will generate the URL and put it in the clipboard. 
Paste it into your browser.  
You will then be prompted to authenticate with your WordPress account and authorize your application. 

#>

$clientID = 'myClientID'
$replyURL = 'https://myWordPressURL.com'
$url = "https://public-api.wordpress.com/oauth2/authorize?client_id=$($clientID)&redirect_uri=$($replyURL)&scope=global%20stats&response_type=code"

$url | clip 

<# 

After authorization use the AuthCode to get an Access Token

#>

Function Get-WordPressAccessToken {
    [CmdletBinding()] 
    param( 
        [Parameter(Mandatory = $true, ValueFromPipeline = $true)] 
        $clientID, 
        [Parameter(Mandatory = $true, ValueFromPipeline = $true)]
        $blogURL, 
        [Parameter(Mandatory = $true, ValueFromPipeline = $true)] 
        $clientSecret, 
        [Parameter(Mandatory = $true, ValueFromPipeline = $true)]
        $authCode
    )

    try { 
        $result = Invoke-RestMethod https://public-api.wordpress.com/oauth2/token `
            -Method Post -ContentType "application/x-www-form-urlencoded" `
            -Body @{
            client_id     = $clientId
            client_secret = $clientSecret
            redirect_uri  = $blogURL
            grant_type    = "authorization_code"
            code          = $authCode
        } -ErrorAction STOP 
        return $result
    }
    catch {
        $_
    }
}

$clientID = 'yourAppClientID'
$clientSecret = 'yourAppClientSecret'
$authCode = 'code_from_browser_authorization'
$replyURL = 'https://myWordPressURL.com'

$accessToken = Get-WordPressAccessToken -ClientID $clientID -blogURL $replyURL -clientSecret $clientSecret -authCode $authCode

<# 

Call the v1.1 API's. e.g Get WordPress Status

#>

Function Get-WordPressStats { 
    [Cmdletbinding()] 
    param( 
        [Parameter(Mandatory = $true, ValueFromPipelineByPropertyName = $true, Position = 0)] 
        [string] $siteID, 
        [Parameter(Mandatory = $true, ValueFromPipelineByPropertyName = $true, Position = 0)] 
        [string] $accessToken
        )

    $stats = Invoke-RestMethod https://public-api.wordpress.com/rest/v1.1/sites/$siteID/stats -Method Get `
        -Headers @{"Authorization" = "Bearer $accessToken" } | Select-object -ExpandProperty Stats 
    return $stats
}

$wpBlogID = '123514446'
Get-WordPressStats -siteID $wpBlogID -accessToken $accessToken.access_token