[TACACS] Add UT to check TACACS will send remote address to server.

[liuh-80]

What I did
Add UT to check TACACS will send remote address to server.

Why I did it
nss-tacplus add a patch to send remote address to server with this PR:sonic-net/sonic-buildimage#12190

To protect the patch, add this UT to check TACACS will send remote address to server.

How I verified it
Pass all UT.

Details if related

[qiluo-msft]

lgtm

lgtm is deprecated. Is this comment needed? #Closed

[qiluo-msft]

W605

I guess you intend to suppress some static code analysis warnings or errors. Could you explain in details so we can review in PR? #Closed

[liuh-80]

Fixed, add detail in comments:

        W605 : Invalid escape sequence. Flake8 can't handle sed command escape sequence, so will report false alert.
        E501 : Line too long. Following sed command difficult to split to multiple line.

[qiluo-msft]

tac_plus.log

I did not get the relationship between

1. server received a 'remote address' from client
2. tac_plus.log matched some pattern.
   Could you explain it in details? #Closed

[liuh-80]

Fixed, add detail in comments:

1. tac_plus server start with '-d 2058' parameter to log received data in following format in tac_plus.log:

    Thu Mar  9 06:26:16 2023 [75483]: data[140] = 0xf8, xor'ed with hash[12] = 0xab -> 0x53
    Thu Mar  9 06:26:16 2023 [75483]: data[141] = 0x8d, xor'ed with hash[13] = 0xc2 -> 0x4f
   

   In above log, the 'data[140] = 0xf8' is received data.

2. Following sed command will extract the received data from tac_plus.log:
   sed -n 's/.-> 0x(..)./\1/p' /var/log/tac_plus.log

   So the result will be:
       f8
       8d
   

3. Following set command will join all received data to hex string:
   sed ':a; N; $!ba; s/\n//g'

   So the result will be:
       f88d.....
   

4. Then the grep command will check if the received hex data containes expected hex string.
   grep '{0}'".format(hex_string)

In our case, because we send remote address to TACACS server, so:

1. we convert remote address to hex string:
   "10.20.0.1" => 31302E32302E302E31
2. We check if the received hex data contains "31302E32302E302E31", if it contains, then we know client do send remote address in TACACS+ package, so the UT passed.

[mssonicbld]

The pre-commit check detected issues in the files touched by this pull request.
The detected issues may be old or new. For new issues, please try to fix them.

For old issues, it is not mandatory to fix them because they were not caused by this change. It is unfair to blame
author of this pull request. But if you can take extra effort to fix the old issues as well, that would be great!

Detailed pre-commit check results:
trim trailing whitespace.................................................Passed
fix end of files.........................................................Passed
check yaml...........................................(no files to check)Skipped
check for added large files..............................................Passed
check python ast.........................................................Passed
flake8...................................................................Failed
- hook id: flake8
- exit code: 1

tests/tacacs/test_accounting.py:141:38: W605 invalid escape sequence '('
tests/tacacs/test_accounting.py:141:42: W605 invalid escape sequence ')'

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   the check by activating the python3 virtual environment in sonic-mgmt docker container or outside of sonic-mgmt
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