This is a little WinForm I created that would output the group membership for a domain user or FBA (Forms-Based Authentication) user on SharePoint.

This is what the form looks like, it gives the option for a domain or FBA user and also checked if the user exists before trying to get the relevant information:

The form first checks if CredSSP is configured on your machine to delegate your credentials to the SharePoint server. The form then loads, waits for your input, validates your input and finally collects the group information for your input.

And finally, this is the code for the Winform. I’ve removed some details as they need to be filled in by you. Enjoy!

#CHECKING CREDSSP SETTINGS
if ((Get-Item  WSMan:\localhost\Client\Auth\CredSSP).value -eq $false){
    #CREDSSP NOT CONFIGURED, EXITING
    Write-Host @"
    
CredSSP is not configured!

Please open an elavated PowerShell prompt and run:

Enable-WSManCredSSP -Role client -DelegateComputer sandsharepointf

"@
    Exit
}else{}

#LOADING ASSEMBLIES
Add-Type -AssemblyName System.Windows.Forms
[System.Windows.Forms.Application]::EnableVisualStyles()

#ICON FOR THE FORM
[string]$icon64=@"
#base64data
"@

#CONVERTING BASE 64 ICON INTO GRAPHIC
$iconstream = [System.IO.MemoryStream][System.Convert]::FromBase64String($icon64)
$iconbmp = [System.Drawing.Bitmap][System.Drawing.Image]::FromStream($iconstream)
$iconhandle = $iconbmp.GetHicon()
$icon = [System.Drawing.Icon]::FromHandle($iconhandle)

#FORM
$SharePoint_Membership_Form                 = New-Object system.Windows.Forms.Form
$SharePoint_Membership_Form.ClientSize      = '400,278'
$SharePoint_Membership_Form.text            = "SharePoint Membership"
$SharePoint_Membership_Form.TopMost         = $false
$SharePoint_Membership_Form.StartPosition   = "centerscreen"
$SharePoint_Membership_Form.Icon            = $icon
$SharePoint_Membership_Form.FormBorderStyle = "Fixed3D"

#USERNAME LABEL
$Username_Label                  = New-Object system.Windows.Forms.Label
$Username_Label.text             = "Enter a username:"
$Username_Label.AutoSize         = $true
$Username_Label.width            = 25
$Username_Label.height           = 10
$Username_Label.location         = New-Object System.Drawing.Point(146,12)

#USERNAME TEXTBOX
$Username_Textbox                = New-Object system.Windows.Forms.TextBox
$Username_Textbox.multiline      = $false
$Username_Textbox.width          = 175
$Username_Textbox.height         = 20
$Username_Textbox.location       = New-Object System.Drawing.Point(115,33)

#VARIABLE FOR KEYDOWN
$Username_Textbox_keydown = {}

#KEYDOWN ASSIGNED
$Username_Textbox_keydown = [System.Windows.Forms.KeyEventHandler]{
    if ($_.keycode -eq 'Enter'){
        $Search_Button.PerformClick()
    }
}

#REGISTER KEYDOWN HANDLER TO USERNAME TEXTBOX
$Username_Textbox.add_keydown($Username_Textbox_keydown)

#DOMAIN RADIO BUTTON
$Domain_User_RB                  = New-Object system.Windows.Forms.RadioButton
$Domain_User_RB.text             = "Domain User"
$Domain_User_RB.AutoSize         = $true
$Domain_User_RB.width            = 104
$Domain_User_RB.height           = 20
$Domain_User_RB.location         = New-Object System.Drawing.Point(120,64)
$Domain_User_RB.Checked          = $true

#SHAREPOINT FBA USER RADIO BUTTON
$FBA_User_RB                     = New-Object system.Windows.Forms.RadioButton
$FBA_User_RB.text                = "FBA User"
$FBA_User_RB.AutoSize            = $true
$FBA_User_RB.width               = 104
$FBA_User_RB.height              = 20
$FBA_User_RB.location            = New-Object System.Drawing.Point(215,64)

#SEARCH BUTTON
$Search_Button                  = New-Object system.Windows.Forms.Button
$Search_Button.text             = "Search"
$Search_Button.width            = 60
$Search_Button.height           = 30
$Search_Button.location         = New-Object System.Drawing.Point(171,89)

#SEPERATOR LINE
$Seperator_Label                 = New-Object system.Windows.Forms.Label
$Seperator_Label.text            = ""
$Seperator_Label.AutoSize        = $false
$Seperator_Label.BorderStyle     = "Fixed3D"
$Seperator_Label.width           = 390
$Seperator_Label.height          = 2
$Seperator_Label.location        = New-Object System.Drawing.Point(5,124)

#OUTPUT TEXTBOX
$Output_Textbox                 = New-Object System.Windows.Forms.TextBox
$Output_Textbox.Multiline       = $true
$Output_Textbox.Width           = 390
$Output_Textbox.Height          = 142
$Output_Textbox.Location        = New-Object System.Drawing.Point(5,131)
$Output_Textbox.ReadOnly        = $true
$Output_Textbox.ScrollBars      = "vertical"

#ADDING CONTROLS TO FORM
$SharePoint_Membership_Form.controls.AddRange(@($Domain_User_RB,$FBA_User_RB,$Seperator_Label,$Username_Label,$Username_Textbox,$Search_Button,$Output_Textbox))

$Search_Button.add_click({

    $Output_Textbox.Text = ""

    #DATE FOR OUTPUT
    $date = Get-Date    
    $username_value = $Username_Textbox.Text
    $Username_Prefix = $null
    $location = #base location

    #SETTING SEARCH VALUES BACK TO FALSE
    $Search_On_AD_User = $false
    $Search_On_FBA_User = $false

    #CHECKING IF USERNAME TEXTBOX IS EMPTY
    if ($Username_Textbox.Text.Length -le 0){
        #IF EMPTY, VARIABLE IS FALSE
        $Output_Textbox.AppendText("$date - $Username cannot be empty! `n")
        $Username_Not_Empty = $false
    }else{
        $Username_Not_Empty = $true
        $Output_Textbox.Text = ""
    }

    #RUNS IF DOMAIN USER RADIO BUTTON IS CHECKED
    if ($Domain_User_RB.Checked -and $Username_Not_Empty){
        try{
            $Output_Textbox.AppendText("$date - Searching for $username_value `n")
            Get-ADUser -Identity $username_value

            $Output_Textbox.AppendText("$date - Found user! `n")

            $Search_On_AD_User = $true
            $Search_On_FBA_User = $false

            $Username_Found = $true

        }catch{
            $Output_Textbox.AppendText("$date - Cannot find domain user `n")
            $Username_Found = $false
        }
    }

    #RUNS IF FBA USER RADIO BUTTON IS CHECKED
    if ($FBA_User_RB.Checked -and $Username_Not_Empty){
        
        $SPAdmin = "sharepoint_admin_user"
        $credential = New-Object System.Management.Automation.PSCredential $SPAdmin,  (Get-Content "$location\sharepoint_admin_user_encrypted_password.txt" | ConvertTo-SecureString )

        $sb = {
            $username = $args[0]
            Add-PSSnapin microsoft.sharepoint.PowerShell
            $user = Get-SPUser -Limit All -Web http://SHAREPOINTSERVER | 
                Where-Object {$_.loginname -like "i:0#.f|fbamembershipprovider|$username"}

            return $user
        }

        $Output_Textbox.AppendText("$date - Trying to find $username_value... `n")

        $invokeoutputfbasearch = Invoke-Command -ScriptBlock $sb -ComputerName SHAREPOINTSERVER -Authentication Credssp -Credential $credential -ArgumentList $username_value

        if ($invokeoutputfbasearch){
            #FOUND USER
            $Username_Found = $true
            $Search_On_FBA_User = $true
            $Search_On_AD_User = $false
            $Output_Textbox.AppendText("$date - Found FBA user!`n")
        }else{
            #NOT FOUND USER
            $Username_Found = $false
            $Output_Textbox.AppendText("$date - Cannot find FBA user `n")
        }
    }

    #ONLY RUNS IF BELOW CONDITIONS ARE MET
    if ($Username_Found -and $Username_Not_Empty){
        #ASSIGNING THE RIGHT USERNAME FORMAT
        if ($Search_On_AD_User){
            $Username_Prefix = "*|DOMAIN_NAME\"
        }else{
            $Username_Prefix = "i:0#.f|fbamembershipprovider|"
        }

        $SPAdmin = "sharepoint_admin_user"
        $credential = New-Object System.Management.Automation.PSCredential $SPAdmin,  (Get-Content "$location\sharepoint_admin_user_encrypted_password.txt" | ConvertTo-SecureString )

        $sb = { 
            $groups = $null
            $prefix = $args[0]
            $username = $args[1]
            Add-PSSnapin Microsoft.SharePoint.PowerShell
            $user = get-SPUser -limit all -web http://SHAREPOINTSERVER | 
                Where-Object { $_.loginname -like "$prefix$username" }
                $SPGroups = get-spsite -limit all | 
                    Select-Object -ExpandProperty rootweb | 
                    Select-Object -ExpandProperty siteusers | 
                    Where-Object { $user.userlogin -eq $_.loginname } | 
                    Select-Object -ExpandProperty groups | 
                    Select-Object -ExpandProperty name
            foreach ($i in $SPGroups){
                $groups = $groups + "     - $i `r`n"
            }
        return $groups
        }

        $Output_Textbox.AppendText("$date - Collecting group info on $username_value... `n")

        $InvokeOutputfinal = Invoke-Command -ScriptBlock $sb -ComputerName SHAREPOINTSERVER -Authentication Credssp -Credential $credential -ArgumentList $Username_Prefix,$username_value

        $Output_Textbox.AppendText("`n")
        $Output_Textbox.AppendText("$InvokeOutputfinal")

    }else{#THIS SERVES ONLY AS A TRAP TO STOP ANYTHING RUNNING
    }
})

#DISPLAYING FORM
[void]$SharePoint_Membership_Form.ShowDialog()