Proposed changes

Improve the certificate validity duration by only using years, days, hours, minutes and seconds (avoiding months), to align to user expectations and avoid the "days in a month" rounding errors in the total duration.

Some examples of the duration in the new format:

• 364d 8h 42m 43s
• 5y 219d 2h 59m
• 2y
• 2h 1m 3s

Background

The humantime crate uses averaged units in the conversion to a human time, so for a duration spanning months, then the remaining hours part of the duration can get skewed unexpectedly (from the users perspective).

For instance, when a certificate is renewed using the Cumulocity Certificate Authority, the new certificate has a validity of 1 year (~365 days if you ignore leap years etc.). When the user downloads a new certificate from Cumulocity, the validity of the certificate is set to 1 year, however the duration displayed is:

Status:        VALID (expires in: 11months 30days 3h 48m 54s)

Where the number of hours remaining is unexpected, as something like 23h 48m 54s would of been more expected (assuming we ignore leap years, total days in a month etc.).

The displaying of the duration in months has the potential to raise more questions, and to avoid having to explain it every time, I'd propose to change to using days as the maximum unit of measurement.

Before (current)

$ tedge cert show
Certificate:   /opt/homebrew/etc/tedge/device-certs/tedge-certificate.pem
Subject:       CN=rmi_macos, O=Thin Edge, OU=Device
Issuer:        C=United States, O=Cumulocity, CN=t9679
Status:        VALID (expires in: 11months 30days 3h 48m 54s)
Valid from:    Thu, 05 Jun 2025 15:50:24 +0000
Valid until:   Fri, 05 Jun 2026 15:50:24 +0000
Serial number: 1749138624770 (0x19740c95102)
Thumbprint:    0FC922ED665081767BC42A180B93A90CA50EAF69

After

$ tedge cert show
Certificate:   /opt/homebrew/etc/tedge/device-certs/tedge-certificate.pem
Subject:       CN=rmi_macos, O=Thin Edge, OU=Device
Issuer:        C=United States, O=Cumulocity, CN=t9679
Status:        VALID (expires in: 364d 23h 57m 43s)
Valid from:    Thu, 05 Jun 2025 15:50:24 +0000
Valid until:   Fri, 05 Jun 2026 15:50:24 +0000
Serial number: 1749138624770 (0x19740c95102)
Thumbprint:    0FC922ED665081767BC42A180B93A90CA50EAF69

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• Documentation Update (if none of the other choices apply)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s. You can activate automatic signing by running just prepare-dev once)
• I ran just format as mentioned in CODING_GUIDELINES
• I used just check as mentioned in CODING_GUIDELINES
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments