Redmine

You are using the REST API, don't you? You need to pass your key with every request...
From the documentation of the REST API:

Authentication¶

Most of the time, the API requires authentication. To enable the API-style authentication, you have to check Enable REST API in Administration -> Settings -> Authentication. Then, authentication can be done in 2 different ways:

• using your regular login/password via HTTP Basic authentication.
• using your API key which is a handy way to avoid putting a password in a script. The API key may be attached to each request in one of the following way:
  • passed in as a "key" parameter
  • passed in as a username with a random password via HTTP Basic authentication
  • passed in as a "X-Redmine-API-Key" HTTP header (added in Redmine 1.1.0)

So either always pass you key along, or use the other methods.