http://www.bouncycastle.org/java.html: The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8.
  • The Legion of the Bouncy Castle Inc. 
package org.bouncycastle.util.encoders;


Convert binary data to and from UrlBase64 encoding.  This is identical to
Base64 encoding, except that the padding character is "." and the other 
non-alphanumeric characters are "-" and "_" instead of "+" and "/".


The purpose of UrlBase64 encoding is to provide a compact encoding of binary
data that is safe for use as an URL parameter. Base64 encoding does not
produce encoded values that are safe for use in URLs, since "/" can be 
interpreted as a path delimiter; "+" is the encoded form of a space; and
"=" is used to separate a name from the corresponding value in an URL 
parameter.

/**
 * Convert binary data to and from UrlBase64 encoding.  This is identical to
 * Base64 encoding, except that the padding character is "." and the other 
 * non-alphanumeric characters are "-" and "_" instead of "+" and "/".
 * <p>
 * The purpose of UrlBase64 encoding is to provide a compact encoding of binary
 * data that is safe for use as an URL parameter. Base64 encoding does not
 * produce encoded values that are safe for use in URLs, since "/" can be 
 * interpreted as a path delimiter; "+" is the encoded form of a space; and
 * "=" is used to separate a name from the corresponding value in an URL 
 * parameter.
 */
public class UrlBase64Encoder extends Base64Encoder
{
    public UrlBase64Encoder()
    {
        encodingTable[encodingTable.length - 2] = (byte) '-';
        encodingTable[encodingTable.length - 1] = (byte) '_';
        padding = (byte) '.';
        // we must re-create the decoding table with the new encoded values.
        initialiseDecodingTable();
    }
}