F5 APM - generate_ga_code

when HTTP_REQUEST {
  set account [URI::query [HTTP::uri] "account"]
  set domain [URI::query [HTTP::uri] "domain"]
  set secret [URI::query [HTTP::uri] "secret"]
  set qr_code [URI::query [HTTP::uri] "qr_code"]

  if { ([HTTP::path] starts_with "/ga_secret_generator") && ($account ne "") && ($domain ne "") } {
    if { [string length $secret] <= 10  } {
      set secret [b64encode [md5 [expr rand()]]]
    }

    set secret [string range $secret 0 9]

    array set b32_alphabet_inv {
       0 A  1 B  2 C  3 D
       4 E  5 F  6 G  7 H
       8 I  9 J 10 K 11 L
      12 M 13 N 14 O 15 P
      16 Q 17 R 18 S 19 T
      20 U 21 V 22 W 23 X
      24 Y 25 Z 26 2 27 3
      28 4 29 5 30 6 31 7
    }

    set secret_b32 ""
    set l [string length $secret]
    set n 0
    set j 0

    # encode loop is outlined in RFC 4648 (http://tools.ietf.org/html/rfc4648#page-8)
    for { set i 0 } { $i < $l } { incr i } {
      set n [expr $n << 8]
      set n [expr $n + [scan [string index $secret $i] %c]]
      set j [incr j 8]

      while { $j >= 5 } {
        set j [incr j -5]
        append secret_b32 $b32_alphabet_inv([expr ($n & (0x1F << $j)) >> $j])
      }
    }

    # pad final input group with zeros to form an integral number of 5-bit groups, then encode
    if { $j > 0 } { append secret_b32 $b32_alphabet_inv([expr $n << (5 - $j) & 0x1F]) }

    # if the final quantum is not an integral multiple of 40, append "=" padding
    set pad [expr 8 - [string length $secret_b32] % 8]
    if { ($pad > 0) && ($pad < 8) } { append secret_b32 [string repeat = $pad] }

    set ga_qr_code_link "https://chart.googleapis.com/chart?chs=200x200&chld=M|0&cht=qr&chl=otpauth://totp/"
    append ga_qr_code_link "$account@$domain"
    append ga_qr_code_link "%3Fsecret%3D"
    append ga_qr_code_link $secret_b32


    set ga_secret_http_resp {<html>
  <body>
    <div align="center">
}

    if { $qr_code eq "yes" } {
      append ga_secret_http_resp "      <img src=\"$ga_qr_code_link\" />\n"
    }

    append ga_secret_http_resp "     <p>account: $account@$domain"
    append ga_secret_http_resp "key (secret): $secret_b32</p>\n    </div>\n  </body>\n</html>"

    HTTP::respond 200 content $ga_secret_http_resp
  } else {
    HTTP::respond 200 content {<html>
  <body>
    <h2><a href="http://goo.gl/edmb2">Google Authenticator</a> key (shared secret) generator</h2>
    <form action="/ga_secret_generator" method="GET">
      <table cellspacing="1" cellpadding="1" border="0">
        <tr>
          <th align="left">account:</th>
          <td><input name="account" type="text" size="10"> @ <input name="domain" type="text" size="20"></td>
        </tr>
        <tr>
          <th align="left">secret:</th>
          <td><input name="secret" type="text" size="10"> *optional 10 character key (additional chars truncated), random secret used if blank</td>
        </tr>
        <tr>
          <th align="left">generate QR code?</th>
          <td><input name="qr_code" type="checkbox" value="yes"> *a request will be made to Google to generate QR code</td>
        </tr>
      </table>
      <input type="submit" value="Submit">
    </form>
  </body>
</html>}
  }
}