That is a valid redirect uri to use. Just keep in mind that it must match exactly in Mashery and what you pass to us in the first authorization call. If you have http://www.domain.com/oauth2cc/constantcontact/123-456-abc in Mashery, the first call you make to us to get the authorization code (or access token, if you're using the client side Oauth2 flow) can't be http://www.domain.com/oauth2cc/constantcontact/123-456-abc?parameter=something (with any parameters appended to the redirect uri).
You can review the OAuth2 authorization process for both server and client flow at the links below.
Best Regards, Shannon Wallace Partner API Support Engineer
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