Decode Base64 String Natively in SQL Server
Figured it out:

SELECT 
    CONVERT
    (
        VARCHAR(MAX), 
        CAST('' AS XML).value('xs:base64Binary(sql:column("BASE64_COLUMN"))', 'VARBINARY(MAX)')
    ) AS RESULT
FROM
    (
        SELECT 'cm9sZToxIHByb2R1Y2VyOjEyIHRpbWVzdGFtcDoxNDY4NjQwMjIyNTcxMDAwIGxhdGxuZ3tsYXRpdHVkZV9lNzo0MTY5ODkzOTQgbG9uZ2l0dWRlX2U3Oi03Mzg5NjYyMTB9IHJhZGl1czoxOTc2NA==' AS BASE64_COLUMN
    ) A


Output:

role:1 producer:12 timestamp:1468640222571000 latlng{latitude_e7:416989394 longitude_e7:-738966210} radius:19764


Just swap out BASE64_COL_NAME for your column name, or you can replace sql:column("BASE64_COLUMN") with sql:variable("@base64variable") if you want to use a declared variable e.g. if you are making a function or something.

It makes use of an XSL transform using built-in XML functionality (since SQL Server 2005)