Register.cshtml

@model RandomPassword.Models.UserRegisterModel

@{
    ViewData["Title"] = "Register";
}

<h2>Register</h2>

<h4>UserRegisterModel</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form asp-action="Register">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <div class="form-group">
                <label asp-for="Username" class="control-label"></label>
                <input asp-for="Username" class="form-control" />
                <span asp-validation-for="Username" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Password" class="control-label"></label>
                <input readonly="readonly" id="passwordInput" asp-for="Password" class="form-control" /> <!-- mark as readonly and add id -->
                <button onclick="generatePassword()">Generate password</button> <!-- create button that triggers the generatePassword() function-->
                <span asp-validation-for="Password" class="text-danger"></span>
            </div>
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-default" />
            </div>
        </form>
    </div>
</div>

<script>
    function generatePassword() {
        event.preventDefault();
        $.get(
            "/Auth/GeneratePassword",
            function (data) {
                document.getElementById("passwordInput").value = data;
            }
        );
    }
</script>