Use GetPelicanUser() to set issuer keys directory's permission group

[h2zh]

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[jhiemstrawisc]

This passes my smell check. Have we confirmed that changing the user to Pelican doesn't prevent us from exporting public keys through the .well-known/ path at our XRootD endpoint?

[h2zh]

This passes my smell check. Have we confirmed that changing the user to Pelican doesn't prevent us from exporting public keys through the .well-known/ path at our XRootD endpoint?

Public key can still be obtained by sending a GET request to https://localhost:8447/.well-known/issuer.jwks (8447 is the port I run Origin), while https://localhost:8443/.well-known/issuer.jwks cannot get the public key before or after this PR(see next comment for update). Am I probing the port and endpoint the same as your expected?

[h2zh]

Alarm cleared! No need to create another issue. I double checked and found out https://localhost:8443/.well-known/issuer.jwks CAN get the public key before AND after this PR. My previous test said "no" because it prompted me to provide a certificate when accessing this endpoint. I just found out that I could just click "cancel" to bypass this blocker and access the public key.