How to Encode and Decode URL-Safe Base64 in ASP.NET Framework?

URL safe Base64 encoding and decoding in ASP.NET Framework

Question:

How to modify the Base64 encoding to comply with the "URL modified Base64" method and solve the "/" character problem that affects UriTemplate matching?

Answer:

Decode modified version of URL Base64:

1. Replace "-" in encoded text with " ".
2. Replace "_" in encoded text with "/".
3. Add the "=" character at the end if necessary. The number of "=" characters depends on the length of the encoded string.

Use a modified version of the URL Base64 to encode:

1. Performs normal Base64 encoding.
2. Replace "=" with an empty string.
3. Replace " " with "-".
4. Replace "/" with "_".

Note:

• Ensure padding is handled correctly during encoding and decoding.
• Encoding logic appends a "0", "1" or "2" to the end of the string, making it suitable for use as a query parameter.
• Consider using the HttpServerUtility class with UrlTokenEncode and UrlTokenDecode methods, which handle URL-safe Base64 encoding and decoding. However, due to character substitution, the result is not a valid Base64 string.

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