<#
    .Synopsis
    Login and retrieve an Access token.

    .Description
    Login and retrieve an Access token from _matrix/client/v3/login. See https://spec.matrix.org/v1.2/client-server-api/#post_matrixclientv3login.

    .Parameter ServerUrl
    URL for the Matrix server to log into, for example "https://matrix.example.com".

    .Parameter Credentials
    PSCredentials Object that contains the Matrix Username and Password for the user you wish to log in with.

    .Example
    # Create a PSCredentials Object
    $creds = Get-Credential
    $token = Get-LoginToken -ServerUrl "https://matrix.example.com" -Credentials $creds
#>
function Get-MatrixLoginToken {
    param(
        [Parameter(Mandatory)]
        [string]$ServerUrl,

        [Parameter(Mandatory)]
        [PSCredential]$Credentials
    )

    $apiPath = "_matrix/client/v3/login"
    $apiMethod = "Post"

    $reqBody = @{
        identifier = @{
            type = "m.id.user"
            user = $Credentials.UserName
        }
        type = "m.login.password"
        password = $Credentials.Password | ConvertFrom-SecureString -AsPlainText
    } | ConvertTo-Json

    $res = Invoke-RestMethod -Uri "$ServerUrl/$apiPath" -Method $apiMethod -Body $reqBody

    $token = $res.access_token | ConvertTo-SecureString

    return $res.access_token
}