Keep in mind that if this is in your program, then it is inherently unsafe. No matter what you do, if the application has the ability to make this secure connection with the information it contains, then this information can be pulled out by an experienced hacker with time and desire.
But are you worried about this level of threat? Obviously, just throwing it into the app.config file is about as low as you. All that should happen is that someone opens the file using text reading and ta-da, you have your credentials.
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