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+# mod_auth_token
+
+This module enables Prosody to authenticate time-based one-time-pin (TOTP) HMAC tokens.
+
+This is an alternative to "external authentication" which avoids the need to
+make a blocking HTTP call to the external authentication service (usually a web application backend).
+
+Instead, the application generates the HMAC token, which is then sent to
+Prosody via the XMPP client and Prosody verifies the authenticity of this
+token.
+
+If the token is verified, then the user is authenticated.
+
+## Luarocks dependencies
+
+You'll need to install the following luarocks
+
+  otp 0.1-5
+  luatz 0.3-1
+
+## How to generate the TOTP seed and shared signing secret
+
+You'll need a shared OTP_SEED value for generating time-based one-time-pin
+(TOTP) values and a shared private key for signing the HMAC token.
+
+You can generate the OTP_SEED value with Python, like so:
+
+    >>> import pyotp
+    >>> pyotp.random_base32()
+    u'XVGR73KMZH2M4XMY'
+
+and the shared secret key as follows:
+
+    >>> import pyotp
+    >>> pyotp.random_base32(length=32)
+    u'JYXEX4IQOEYFYQ2S3MC5P4ZT4SDHYEA7'
+
+## Configuration
+
+Firest you need to enable the relevant modules to your Prosody.cfg file.
+
+Look for the line `modules_enabled` (either globally or for your
+particular `VirtualHost`), and then add the following to tokens:
+
+    modules_enabled = {
+        -- Token authentication
+            "auth_token";
+            "sasl_token";
+    }
+
+The previously generated token values also need to go into your Prosody.cfg file:
+
+    authentication = "token";
+    token_secret = "JYXEX4IQOEYFYQ2S3MC5P4ZT4SDHYEA7";
+    otp_seed = "XVGR73KMZH2M4XMY";
+
+The application that generates the tokens also needs access to these values.
+
+For an example on how to generate a token, take a look at the `generate_token`
+function in the `test_token_auth.lua` file inside this directory.
+
+## Custom SASL auth
+
+This module depends on a custom SASL auth mechanism called X-TOKEN and which
+is provided by the file `mod_sasl_token.lua`.
+
+Prosody doesn't automatically pick up this file, so you'll need to update your
+configuration file's `plugin_paths` to link to this subdirectory (for example
+to `/usr/lib/prosody-modules/mod_auth_token/`).
+
+## Generating the token
+
+Here's a Python snippet showing how you can generate the token that Prosody
+will then verify:
+
+    import base64
+    import pyotp
+    import random
+
+    # Constants
+    OTP_INTERVAL = 30
+    OTP_DIGITS = 8
+
+    jid = '{}@{}'.format(username, domain)
+
+    otp_service = pyotp.TOTP(
+        OTP_SEED,  # OTP_SEED must be set to the value generated previously (see above)
+        digits=OTP_DIGITS,
+        interval=OTP_INTERVAL
+    )
+    otp = otp_service.generate_otp(otp_service.timecode(datetime.utcnow()))
+
+    nonce = ''.join([str(random.randint(0, 9)) for i in range(32)])
+    string_to_sign = otp + nonce + jid
+    signature = hmac.new(token_secret, string_to_sign, hashlib.sha256).digest()
+    token = u"{} {}".format(otp+nonce, base64.b64encode(signature))
+