This service makes it possible to read the most recent location from a KML stream, and form a request containing that location to an arbitrarily templated target URL. To contribute or fork this project see the github repo.
The original motivation for this is to forward an InReach location to a CalTopo locator, without needing to upgrade to a professional InReach subscription plan. In the Social tab of Garmin Explore, you can get a URL to a KML feed (not the one for Google Earth), containing your InReach's most recent tracking points. This is the KML URL.
Get the Target URL from CalTopo by adding a Live tracker object of type "Fleet, Email, other". Follow the instructions and copy the provided API endpoint URL, replacing the sample latitude and longitude with {lat} and {long}, respectively.
Each locator will be automatically deleted after the specified number of days. You may provide a password with which your locators can be edited before they expire. Each locator has its own password, chosen at the time of creation.
Every 5 minutes, the server will check which locations need to be updated, and send a new request to their corresponding target URLs. A locator will be updated when the last update was more than frequency minutes in the past. However, note that locators with frequency values of less than 5 minutes will only be updated every five minutes. It's best to stick with multiples of 5 for the frequency value.