C Driver: Heap overflow via 32-bit length wrap of the URI username in Windows Kerberos auth message wrapping

A 32-bit integer wraparound in the MongoDB C Driver's Windows-only Kerberos/SSPI authentication code can cause an undersized heap buffer to be allocated when an excessively long credential value is supplied in the client's connection configuration. A party able to control that client-side configuration, in conjunction with the affected authentication mechanism, can cause the driver to write outside the bounds of the allocated buffer. This may result in corruption of client process memory and denial of service of the client application. The issue affects only client builds compiled with the Windows-native authentication backend.