Authentication error "invalid vm name" for VMSS instances

[notheotherben]

The regex name validations introduced in #153 places requirements on VM names which are incompatible with the way in which VMSS instance names are constructed (namely they use the VMSS name and append _NNN to uniqely identify instances within the VMSS).

As a consequence, running the v1.18.0 Vault server results in the agent being unable to authenticate using this plugin when running on VMSS instances. Reverting to Vault v1.17.6 resolves the issue (running Vault server v1.17.6 with agents at v1.18.0 works correctly, so this is an issue on the server side - reverting to older versions of the agent doesn't resolve the issue).

Example Log Line (Redacted)

{"@level":"error","@message":"error authenticating","@module":"agent.auth.handler","@timestamp":"2024-10-11T20:00:00.000000Z","backoff":{},"error":"Error making API request.\n\nURL: PUT https://vault:8200/v1/auth/azure/login\nCode: 400. Errors:\n\n* invalid vm name \"vmssname_0\""}

[kpcraig]

Sorry about that! #172 should resolve the issue with the underscores in vmss names. It is included in the 0.19.2 version of this plugin, which itself is included in v1.18.2 of Vault.