pop3: Added support for SASL based authentication mechanism detection

Added support for detecting the supported SASL authentication mechanisms
via the AUTH command. There are two ways of detecting them, either by
using the AUTH command, that will return -ERR if not supported or by
using the CAPA command which will return SASL and the list of mechanisms
if supported, not include SASL if SASL authentication is not supported
or -ERR if the CAPA command is not supported. As such it seems simpler
to use the AUTH command and fallback to normal clear text authentication
if the the command is not supported.

Additionally updated the test cases to return -ERR when the AUTH command
is encountered. Additional test cases will be added when support for the
individual authentication mechanisms is added.

tests/data/test808

@@ -10,6 +10,7 @@ LIST
 # Server-side
 <reply>
 <servercmd>
+REPLY AUTH -ERR unsupported command
 REPLY LIST +OK 808 100
 </servercmd>
 </reply>
@@ -32,6 +33,7 @@ pop3://%HOSTIP:%POP3PORT/808 -l -u user:secret
 # Verify data after the test has been "shot"
 <verify>
 <protocol>
+AUTH
 USER user
 PASS secret
 LIST 808

tests/data/test809

@@ -11,6 +11,7 @@ FAILURE
 # Server-side
 <reply>
 <servercmd>
+REPLY AUTH -ERR unsupported command
 REPLY LIST -ERR no such message
 </servercmd>
 </reply>
@@ -36,6 +37,7 @@ pop3://%HOSTIP:%POP3PORT/809 -l -u user:secret
 56
 </errorcode>
 <protocol>
+AUTH
 USER user
 PASS secret
 LIST 809

tests/data/test810

@@ -13,6 +13,7 @@ LIST
 # packets
 <servercmd>
 SLOWDOWN
+REPLY AUTH -ERR unsupported command
 </servercmd>
 # When doing LIST, we get the default list output hard-coded in the test
 # POP3 server
@@ -41,6 +42,7 @@ pop3://%HOSTIP:%POP3PORT/ -u user:secret
 # Verify data after the test has been "shot"
 <verify>
 <protocol>
+AUTH
 USER user
 PASS secret
 LIST

tests/data/test811

@@ -10,6 +10,7 @@ LIST
 # Server-side
 <reply>
 <servercmd>
+REPLY AUTH -ERR unsupported command
 REPLY LIST +OK but no messages\r\n.
 </servercmd>
 <datacheck>
@@ -34,6 +35,7 @@ pop3://%HOSTIP:%POP3PORT/ -u user:secret
 # Verify data after the test has been "shot"
 <verify>
 <protocol>
+AUTH
 USER user
 PASS secret
 LIST

tests/data/test812

@@ -11,6 +11,7 @@ FAILURE
 # Server-side
 <reply>
 <servercmd>
+REPLY AUTH -ERR unsupported command
 REPLY RETR -ERR no such message
 </servercmd>
 </reply>
@@ -36,6 +37,7 @@ pop3://%HOSTIP:%POP3PORT/812 -u user:secret
 56
 </errorcode>
 <protocol>
+AUTH
 USER user
 PASS secret
 RETR 812

tests/data/test813

@@ -10,6 +10,7 @@ FAILURE
 # Server-side
 <reply>
 <servercmd>
+REPLY AUTH -ERR unsupported command
 REPLY PASS -ERR invalid login
 </servercmd>
 </reply>
@@ -35,6 +36,7 @@ pop3://%HOSTIP:%POP3PORT/813 -u user:wrong
 67
 </errorcode>
 <protocol>
+AUTH
 USER user
 PASS wrong
 QUIT

tests/data/test815

@@ -9,6 +9,9 @@ RETR
 #
 # Server-side
 <reply>
+<servercmd>
+REPLY AUTH -ERR unsupported command
+</servercmd>
 <data>
 From: me@somewhere
 To: fake@nowhere
@@ -49,6 +52,7 @@ pop3://%HOSTIP:%POP3PORT/815 -u user:secret
 # Verify data after the test has been "shot"
 <verify>
 <protocol>
+AUTH
 USER user
 PASS secret
 RETR 815