fix #4074: increase API OpenID code size limit to 2048

fix #4074: increase API OpenID code size limit to 2048

Azure AD seems to have a variable authorization code size, depending on
the browser state according to one report in bug #4074 [0].

Sometimes the size is greater than our current limit of 1024, so
increase it to 2048.

The RFC [1] mentions that there is no limit to the code size, but based on
current experience, a size limit of 2048 might be enough for every
current OpenID Connect provider.

[0] https://bugzilla.proxmox.com/show_bug.cgi?id=4074
[1] https://datatracker.ietf.org/doc/html/rfc6749#section-4.1.2

Signed-off-by: Mira Limbeck <m.limbeck@proxmox.com>
[w.bumiller@proxmox.com: bump to 4096]
Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>