Es una opción de web.config, dentro de <system.web>.
Un ejemplo:
<membership>
      <providers>
        <remove name="AspNetSqlMembershipProvider" />
        <add connectionStringName="LocalSqlServer" enablePasswordRetrieval="false"
         enablePasswordReset="true" requiresQuestionAndAnswer="true" applicationName="/"
         requiresUniqueEmail="false" passwordFormat="Hashed" maxInvalidPasswordAttempts="5"
         minRequiredPasswordLength="3" minRequiredNonalphanumericCharacters="0"
         passwordAttemptWindow="10" passwordStrengthRegularExpression=""
         name="AspNetSqlMembershipProvider" type="System.Web.Security.SqlMembershipProvider, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
      </providers>
    </membership>