support set "forever" on valid_before field of the certificate

[gzm55]

when sign by ssh-keygen, in valid_before field, the "forever" is translated to 2**64-1. This behavior is not supported by sshkey-tools now.

[scheibling]

I'll put it in the next update (EOW) along with restoring the functionality for choosing the RSA Algo. Thanks for the feedback!

Edit: In the meantime, you can pass integers to that field on creation as well. The plan is to add strings as allowed types and to parse them with something like pytimeparse

[scheibling]

Fixed in #17 , you can now specify a string like "2w", "1d4h" or similar (according to the specification in pytimeparse2, including "forever" which will set the expiration time to MAX_INT64.

Also updated the docs in #18

It'll be included in upcoming release 0.9.2 on pypi

[gzm55]

@scheibling MAX_INT64 is 2**64, which is too large for 64 bit integer. The stack is

    return pack(">Q", value)
           ^^^^^^^^^^^^^^^^^
struct.error: int too large to convert

It seems that MAX_INT64 - 1 should be used.

[scheibling]

Saw this earlier but it seems it managed to slip my mind.. I'll fix it, thanks for checking. Have somewhere on my to-do list to add some more tests as well to catch things like this.

[scheibling]

Resolved through #17 and bugs in #20 #21