Symptoms/Context:
I am using following curl:
curl -X POST -H "Content-type: application/json" -H "Authorization: LC apiKey=ag_vgxK6w24o5eL" -d '{"text":"سلام دنیا", "from":"fa", "to":"eng"}' http://10.X.X.X:8001/api/v1 Get exception: Not Authorized
 you'll find REST API documentation under SDL_ETS_7_x_x_win64_installer\docs\api\rest\
Once SDL ETS is installed you can find REST API under :
c:\Program Files\SDL\SDL ETS\docs\
correct REST API call :
curl -X POST -u ag_vgxK6w24o5eL: -d mode="text" -d sourceLanguageId="per" -d targetLanguageId="fra" -d text="2LPZhNin2YUg2K/ZhtuM2Kc=" 10.X.X.X:8001/.../quick"
-the source text has to be Base64 encoded.