fix: support multiple SSHPubKey records per user

There was one blazing issue with the previous implementation regardless
of the multiple records: we were generating fingerprints by storing
the key into a file and reading it with ssh-keygen. This is absolutely
terrible and was not meant to be left around (it was forgotten, my bad).

Took this opportunity to clean up a few things:
- simplify pubkey validation
- centralize things a bit better

Signed-off-by: Kevin Morris <kevr@0cost.org>

test/test_ssh_pub_key.py

@@ -1,3 +1,5 @@
+from subprocess import PIPE, Popen
+
 import pytest
 
 from aurweb import db
@@ -61,8 +63,12 @@ def test_pubkey_cs(user: User):
 
 
 def test_pubkey_fingerprint():
-    assert get_fingerprint(TEST_SSH_PUBKEY) is not None
+    proc = Popen(["ssh-keygen", "-l", "-f", "-"], stdin=PIPE, stdout=PIPE)
+    out, _ = proc.communicate(TEST_SSH_PUBKEY.encode())
+    expected = out.decode().split()[1].split(":", 1)[1]
+    assert get_fingerprint(TEST_SSH_PUBKEY) == expected
 
 
 def test_pubkey_invalid_fingerprint():
-    assert get_fingerprint("ssh-rsa fake and invalid") is None
+    with pytest.raises(ValueError):
+        get_fingerprint("invalid-prefix some-fake-content")