functions/Rename-DbaLogin.ps1

function Rename-DbaLogin {
    <#
    .SYNOPSIS
        Rename-DbaLogin will rename login and database mapping for a specified login.
 
    .DESCRIPTION
        There are times where you might want to rename a login that was copied down, or if the name is not descriptive for what it does.
 
        It can be a pain to update all of the mappings for a specific user, this does it for you.
 
    .PARAMETER SqlInstance
        Source SQL Server.You must have sysadmin access and server version must be SQL Server version 2000 or greater.
 
    .PARAMETER Destination
        Destination Sql Server. You must have sysadmin access and server version must be SQL Server version 2000 or greater.
 
    .PARAMETER SqlCredential
        Login to the target instance using alternative credentials. Accepts PowerShell credentials (Get-Credential).
 
        Windows Authentication, SQL Server Authentication, Active Directory - Password, and Active Directory - Integrated are all supported.
 
        For MFA support, please use Connect-DbaInstance.
 
    .PARAMETER Login
        The current Login on the server - this list is auto-populated from the server.
 
    .PARAMETER NewLogin
        The new Login that you wish to use. If it is a windows user login, then the SID must match.
 
    .PARAMETER Confirm
        Prompts to confirm actions
 
    .PARAMETER WhatIf
        Shows what would happen if the command were to run. No actions are actually performed.
 
    .PARAMETER EnableException
        By default, when something goes wrong we try to catch it, interpret it and give you a friendly warning message.
        This avoids overwhelming you with "sea of red" exceptions, but is inconvenient because it basically disables advanced scripting.
        Using this switch turns this "nice by default" feature off and enables you to catch exceptions with your own try/catch.
 
    .NOTES
        Tags: Login
        Author: Mitchell Hamann (@SirCaptainMitch)
 
        Website: https://dbatools.io
        Copyright: (c) 2018 by dbatools, licensed under MIT
        License: MIT https://opensource.org/licenses/MIT
 
    .LINK
        https://dbatools.io/Rename-DbaLogin
 
    .EXAMPLE
        PS C:\>Rename-DbaLogin -SqlInstance localhost -Login DbaToolsUser -NewLogin captain
 
        SQL Login Example
 
    .EXAMPLE
        PS C:\>Rename-DbaLogin -SqlInstance localhost -Login domain\oldname -NewLogin domain\newname
 
        Change the windowsuser login name.
 
    .EXAMPLE
        PS C:\>Rename-DbaLogin -SqlInstance localhost -Login dbatoolsuser -NewLogin captain -WhatIf
 
        WhatIf Example
 
    #>

    [CmdletBinding(DefaultParameterSetName = "Default", SupportsShouldProcess)]
    param (
        [parameter(Mandatory)]
        [DbaInstanceParameter[]]$SqlInstance,
        [PSCredential]$SqlCredential,
        [parameter(Mandatory)]
        [string]$Login,
        [parameter(Mandatory)]
        [string]$NewLogin,
        [switch]$EnableException
    )

    process {
        foreach ($instance in $SqlInstance) {
            try {
                $server = Connect-SqlInstance -SqlInstance $instance -SqlCredential $sqlcredential
            } catch {
                Stop-Function -Message "Error occurred while establishing connection to $instance" -Category ConnectionError -ErrorRecord $_ -Target $instance -Continue
            }

            $Databases = $server.Databases | Where-Object IsAccessible
            $currentLogin = $server.Logins[$Login]

            if ($Pscmdlet.ShouldProcess($SqlInstance, "Changing Login name from [$Login] to [$NewLogin]")) {
                try {
                    $dbenums = $currentLogin.EnumDatabaseMappings()
                    $currentLogin.rename($NewLogin)
                    [pscustomobject]@{
                        ComputerName  = $server.ComputerName
                        InstanceName  = $server.ServiceName
                        SqlInstance   = $server.DomainInstanceName
                        Database      = $null
                        PreviousLogin = $Login
                        NewLogin      = $NewLogin
                        Status        = "Successful"
                    }
                } catch {
                    $dbenums = $null
                    [pscustomobject]@{
                        ComputerName  = $server.ComputerName
                        InstanceName  = $server.ServiceName
                        SqlInstance   = $server.DomainInstanceName
                        Database      = $null
                        PreviousLogin = $Login
                        NewLogin      = $NewLogin
                        Status        = "Failure"
                    }
                    Stop-Function -Message "Failure" -ErrorRecord $_ -Target $login
                }
            }

            foreach ($db in $dbenums) {
                $db = $databases[$db.DBName]
                $user = $db.Users[$Login]
                Write-Message -Level Verbose -Message "Starting update for $db"

                if ($Pscmdlet.ShouldProcess($SqlInstance, "Changing database $db user $user from [$Login] to [$NewLogin]")) {
                    try {
                        $oldname = $user.name
                        $user.Rename($NewLogin)
                        [pscustomobject]@{
                            ComputerName = $server.ComputerName
                            InstanceName = $server.ServiceName
                            SqlInstance  = $server.DomainInstanceName
                            Database     = $db.name
                            PreviousUser = $oldname
                            NewUser      = $NewLogin
                            Status       = "Successful"
                        }

                    } catch {
                        Write-Message -Level Warning -Message "Rolling back update to login: $Login"
                        $currentLogin.rename($Login)

                        [pscustomobject]@{
                            ComputerName = $server.ComputerName
                            InstanceName = $server.ServiceName
                            SqlInstance  = $server.DomainInstanceName
                            Database     = $db.name
                            PreviousUser = $NewLogin
                            NewUser      = $oldname
                            Status       = "Failure to rename. Rolled back change."
                        }
                        Stop-Function -Message "Failure" -ErrorRecord $_ -Target $NewLogin
                    }
                }
            }
        }
    }
}