How to translate this JS to C#

Hi..
I have the following JS code..
How do I translate this to C#?

I think Dictionary is the same as MAP in C#, what about parmas.get  and keyset??

(getAuthTemplateTag returns a constant- not an issue)

thx

public final String createAuthTemplateXML(Map<String, String> params) {
            StringBuilder sb = new StringBuilder();
            sb.append("<authRequest>").append("\n").append("<")
                        .append(getAuthTemplateTag()).append(">").append("\n");

            for (String key : params.keySet()) {
                  sb.append("<").append(key).append(">").append(params.get(key))
                              .append("</").append(key).append(">").append("\n");
            }
            sb.append("</").append(getAuthTemplateTag()).append(">").append("\n")
                        .append("</authRequest>").append("\n");

            return sb.toString();
      }