The Url64 encoding scheme 

Url64 is a variant of the widely used Base64-encoding scheme that does not use the slash-character to enable embedding Url64 encoded strings within regular URI path segments.

The Url64 encoding scheme is indentical to the Base64 encoding scheme as described in RFC 1521 (Section 5.2) with the exception that the in the output encoding table the “-“ character is used instead of the “/” character to avoid conflicts with the “/” as URI-path segment delimiter.