Kibana crashing when xpack.security.sessionTimeout is set to a string

[jportner]

Kibana version: 7.x / 8.0

Describe the bug: Kibana crashes when using a string to specify a session timeout

Steps to reproduce:

Set config:

xpack.security.sessionTimeout: "12345"

Run Kibana:

 FATAL  Error: [config validation of [xpack.security].session.idleTimeout]: types that failed validation:
- [config validation of [xpack.security].session.idleTimeout.0]: Failed to parse [12345] as time value. Format must be <count>[ms|s|m|h|d|w|M|Y] (e.g. '70ms', '5s', '3d', '1Y')
- [config validation of [xpack.security].session.idleTimeout.1]: expected value to equal [null] but got [12345]

This doesn't happen if you use a sessionTimeout without quotes:

xpack.security.sessionTimeout: 12345

Any additional context: Unintentional breaking change caused by #53768. Previous Kibana behavior would read a string and coerce it to a number.

Reported by @nachogiljaldo (thanks!)

[elasticmachine]

Pinging @elastic/kibana-security (Team:Security)

[jportner]

I think the correct fix for this is to change duration to handle strings that don't have a time format qualifier, and assume that those strings are milliseconds. @azasypkin what do you think?

[mieciu]

I've been hit by this today trying to run 7.6.0-SNAPSHOT in Cloud.

strings that don't have a time format qualifier, and assume that those strings are milliseconds

Sounds good. Backwards compatible plus AFAIR also consistent with other settings we have (xpack.reporting.capture.loadDelay, elasticsearch.requestTimeout to name a few). 👍