Which is the maximum number of keys in authorized_keys file?
There is no limit to the number of entries in the file. From the source code
auth2-pubkey.c
/* return 1 if user allows given key */
static int
user_key_allowed2(struct passwd *pw, Key *key, char *file)
{ ...
while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
char *cp, *key_options = NULL;
As you can see this simply loops over the file until read_keyfile_line returns -1.
There is no limit, but finding the correct key will be slow, like GREPing a large text file.