Documentation link to Kerberos installation instructions is now out-of-date

[da1910]

The requests-kerberos package we depend on previously provided some instructions to setup Kerberos authentication on different platforms. It now does not, so the help link is of no value.

We should either find a permanent source of instructions for supported platforms, or we should produce our own for those platforms we officially support.

[da1910]

A quick scan of the packages I'm aware of that wrap the GSSAPI reveals no attempt at a guide for installation and configuration.

pykrb5 lists the following build-time arguments that are variously set or not set by python-gssapi which is a dependency of requests-kerberos on linux:

• KRB5_KRB5CONFIG
• KRB5_MAIN_LIB
• KRB5_COMPILER_ARGS
• KRB5_LINKER_ARGS
• KRB5_SKIP_MODULE_CHECK
• KRB5_CYTHON_TRACING
• KRB5_MACOS_HEIMDAL_DIR

See: https://github.com/jborean93/pykrb5

It's possible that with the appropriate header packages installed python-gssapi will set these appropriately, but we should check our officially supported platforms at least:

• Ubuntu 1804
• Debian 9.11
• OpenSUSE / SLES 15.2
• CentOS 7.9 / RHEL equivalent

@Andy-Grigg is it worth checking how to do this for MacOS as well?

[Andy-Grigg]

Current thinking for this ticket is that we test on all packages once and check that it should work, given a correctly setup kerberos evironment.

We have automated tests for Ubuntu 1804, but we can test locally for the other three and update the documentation accordingly.