Keys written with incorrect username when SAML

[russjones]

Problem

When using an external identity provider, tsh login writes keys to disk with the wrong name (name of the local Linux user) instead of the username returned by the identity provide. This was fixed in #1642 but not backported to branch/2.4.

$ ./tsh.sh --proxy=localhost login
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[...]

You are now logged in

$ tree ~/.tsh/
/Users/rjones/.tsh/
├── keys
│   └── localhost
│       ├── rjones
│       ├── rjones-cert.pub
│       └── rjones.pub
├── known_hosts
├── localhost.yaml
└── profile -> localhost.yaml

$ ./tsh.sh --proxy=localhost ls
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[...]

Node Name Node ID                              Address        Labels                                                        
--------- ------------------------------------ -------------- ------------------------------------------------------------- 
proxy     30465e32-7b48-4d8f-9b24-be80c2dd77c9 127.0.0.1:3022 arch=fork/exec /bin/uname: no such file or directory output:  

$ tree ~/.tsh/
/Users/rjones/.tsh/
├── cache
│   └── localhost:3023
│       └── example.com
│           └── namespaces
│               └── default
│                   └── nodes
│                       └── 30465e32-7b48-4d8f-9b24-be80c2dd77c9
├── keys
│   └── localhost
│       ├── rjones
│       ├── rjones-cert.pub
│       ├── rjones.pub
│       ├── [email protected]
│       ├── [email protected]
│       └── [email protected]
├── known_hosts
├── localhost.yaml
└── profile -> localhost.yaml

8 directories, 10 files

Proposed Solution

Backport the chunk of #1642 where the username in the local agent is set if using an external identity provider.

[russjones]

Fixed in #1750.