Trechos de man ssh-keygen :
-I certificate_identity
Specify the key identity when signing a public key. Please see the CERTIFICATES section for details.
CERTIFICATES
ssh-keygen supports signing of keys to produce certificates that may be used for user or host authentication. Certificates consist of a public key, some
identity information, zero or more principal (user or host) names and a set of options that are signed by a Certification Authority (CA) key. Clients or
servers may then trust only the CA key and verify its signature on a certificate rather than trusting many user/host keys. Note that OpenSSH certifi‐
cates are a different, and much simpler, format to the X.509 certificates used in ssl(8).
ssh-keygen supports two types of certificates: user and host. User certificates authenticate users to servers, whereas host certificates authenticate
server hosts to users. To generate a user certificate:
$ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
The resultant certificate will be placed in /path/to/user_key-cert.pub. A host certificate requires the -h option:
$ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
The host certificate will be output to /path/to/host_key-cert.pub.
It is possible to sign using a CA key stored in a PKCS#11 token by providing the token library using -D and identifying the CA key by providing its pub‐
lic half as an argument to -s:
$ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id user_key.pub
In all cases, key_id is a "key identifier" that is logged by the server when the certificate is used for authentication.
Certificates may be limited to be valid for a set of principal (user/host) names. By default, generated certificates are valid for all users or hosts.
To generate a certificate for a specified set of principals:
$ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
$ ssh-keygen -s ca_key -I key_id -h -n host.domain host_key.pub
Additional limitations on the validity and use of user certificates may be specified through certificate options. A certificate option may disable fea‐
tures of the SSH session, may be valid only when presented from particular source addresses or may force the use of a specific command. For a list of
valid certificate options, see the documentation for the -O option above.
Finally, certificates may be defined with a validity lifetime. The -V option allows specification of certificate start and end times. A certificate
that is presented at a time outside this range will not be considered valid. By default, certificates are valid from UNIX Epoch to the distant future.
For certificates to be used for user or host authentication, the CA public key must be trusted by sshd(8) or ssh(1). Please refer to those manual pages
for details.
Nota:
In all cases, key_id is a "key identifier" that is logged by the server when the certificate is used for authentication.
E no seu link, afirma:
-I: This is a name that is used to identify the certificate. It is used for logging purposes when the certificate is used for authentication.
Ao usar certificados para autenticação, eles possuem chaves para identificar o certificado específico de autenticação. Isto é dado qualquer nome que você gostaria de chamar meu my-new-cert-id e o certificado será construído com esse id e usado para acessar o meu certificado de autenticação.
Observe que nesse link você usou dois nomes diferentes de -I para escolher o que você gosta.
Função de -I : ssh-keygen suporta a assinatura de chaves para produzir certificados que podem ser usados para autenticação de usuário ou host. Usado quando você precisa usar certificados para autenticação.
Valor de -I : : qualquer nome que você goste