if (Membership.ValidateUser(TextBox1.Text, TextBox2.Text))
        {
            FormsAuthentication.RedirectFromLoginPage(TextBox1.Text, true);
        }

<?xml version="1.0"?>
<!--
  Дополнительные сведения о настройке приложения ASP.NET см. на странице
  https://go.microsoft.com/fwlink/?LinkId=169433.
  -->
<configuration>
  <!--
    Описание изменений web.config см. по адресу http://go.microsoft.com/fwlink/?LinkId=235367.
 
    Следующие атрибуты можно установить с помощью тега <httpRuntime>.
      <system.Web>
        <httpRuntime targetFramework="4.7" />
      </system.Web>
  -->
  <system.web>
    <sessionState timeout="3000"/>
    <customErrors mode="Off"/>
    <compilation debug="true" targetFramework="4.7" />
    <httpRuntime targetFramework="4.7" />
    <pages styleSheetTheme="Skin1" enableViewStateMac="false" validateRequest="false" enableEventValidation="false" viewStateEncryptionMode ="Never"/>
    <authentication mode="Forms" >
      <forms name="MyCookieName" loginUrl="/Call/ChangeUser.aspx" timeout="3000" slidingExpiration="true" cookieless="AutoDetect" protection="None"
        requireSSL="false" enableCrossAppRedirects="false" defaultUrl="/Call/ChangeUser.aspx" path="/">
 
      </forms>
    </authentication>
    <authorization>
      <allow users="?"/>
      <allow users="*"/>
    </authorization>
    <membership defaultProvider="MyMembershipProvider">
      <providers>
        <add connectionStringName="connSqlServer" applicationName="myapp" minRequiredPasswordLength="5" minRequiredNonalphanumericCharacters="0"
          passwordFormat="Clear" description="Необязательно описание поставщика членства" enablePasswordReset="true" enablePasswordRetrieval="false"
          maxInvalidPasswordAttempts="20" passwordAttemptWindow="20" requiresQuestionAndAnswer="false" requiresUniqueEmail="true" name="MyMembershipProvider"
          type="System.Web.Security.SqlMembershipProvider"/>
      </providers>
    </membership>
    <roleManager enabled="true" cacheRolesInCookie="true" cookieName=".MyRolesCookie"
      defaultProvider="MyRoleProvider">
      <providers>
        <add connectionStringName="connSqlServer" applicationName="myapp"
          name="MyRoleProvider" type="System.Web.Security.SqlRoleProvider" />
      </providers>
    </roleManager>
  </system.web>
  <!-- заглушка от ошибки -->
  <appSettings>
    <add key="ValidationSettings:UnobtrusiveValidationMode" value="None"/>
  </appSettings>
  <connectionStrings>
    <add name="connSqlServer" connectionString="Data Source=myapp.ru;Initial Catalog=u0640305_myapp;User Id=admin;Password=12345;Connect Timeout=30"/>
  </connectionStrings>
  <system.codedom>
    <compilers>
      <compiler language="c#;cs;csharp" extension=".cs"
        type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
        warningLevel="4" compilerOptions="/langversion:default /nowarn:1659;1699;1701"/>
      <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb"
        type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
        warningLevel="4" compilerOptions="/langversion:default /nowarn:41008 /define:_MYTYPE=\"Web\" /optionInfer+"/>
    </compilers>
  </system.codedom>
</configuration>