[PATCH] Fix IMAP auth_crm MD5 digest of secret to use memcpy().

For a secret longer that MD5_BLOCK_LEN, an MD5 digest is used
instead.  However, mutt was incorrectly using strfcpy() on the raw
binary value returned by md5_buffer, instead of memcpy().  This could
result in authentication failing.

This likely hasn't been a big issue because:
1. CRAM-MD5 is not used much anymore
2. Most people likely don't have a password length greater than 64
   bytes.
3. It relies on the case of an exactly aligned 0x00 byte in the digest
   result, which is likely also infrequent.

Thanks to [email protected] for the security report.
---
This is 5 in the list evilrabbit sent.

 imap/auth_cram.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/imap/auth_cram.c b/imap/auth_cram.c
index 6080ea47..6a265de6 100644
--- a/imap/auth_cram.c
+++ b/imap/auth_cram.c
@@ -149,7 +149,7 @@ static void hmac_md5 (const char* password, char* challenge,
   if (secret_len > MD5_BLOCK_LEN)
   {
     md5_buffer (password, secret_len, hash_passwd);
-    strfcpy ((char*) secret, (char*) hash_passwd, MD5_DIGEST_LEN);
+    memcpy(secret, hash_passwd, MD5_DIGEST_LEN);
     secret_len = MD5_DIGEST_LEN;
   }
   else
-- 
2.53.0