How do I encode and decode a base64 string?

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How do I return a base64 encoded string given a string?

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How do I decode a base64 encoded string into a string?

Encode

public static string Base64Encode(string plainText) 
{
    var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(plainText);
    return System.Convert.ToBase64String(plainTextBytes);
}

Decode

public static string Base64Decode(string base64EncodedData) 
{
    var base64EncodedBytes = System.Convert.FromBase64String(base64EncodedData);
    return System.Text.Encoding.UTF8.GetString(base64EncodedBytes);
}

Stack Overflow Q#11743160, score: 2510