Add readme.

LICENSE

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+The MIT License (MIT)
+
+Copyright (c) 2022 Jared Hanson
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

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+# passport-ethereum-siwe
+
+[Passport](https://www.passportjs.org/) strategy for authenticating
+with [Sign-In with Ethereum](https://login.xyz/).
+
+This module lets you authenticate using [Sign-In with Ethereum](https://eips.ethereum.org/EIPS/eip-4361)
+in your Node.js applications.  By plugging into Passport, Ethereum
+authentication can be easily and unobtrusively integrated into any application
+or framework that supports [Connect](https://github.com/senchalabs/connect#readme)-style
+middleware including [Express](https://expressjs.com/).
+
+## Install
+
+```sh
+$ npm install passport-ethereum-siwe
+```
+
+## Usage
+
+The Ethereum authentication strategy authenticates users using an Ethereum
+wallet.
+
+The strategy takes a `verify` function as an argument, which accepts `address`
+as an argument.  `address` is the user's Ethereum address.  When authenticating
+a user, this strategy obtains this information from a message signed by the
+user's wallet.
+
+The `verify` function is responsible for determining the user to which the
+address belongs.  In cases where the account is logging in for the first time, a
+new user record is typically created automatically.  On subsequent logins, the
+existing user record will be found via its relation to the address.
+
+Because the `verify` function is supplied by the application, the app is free to
+use any database of its choosing.  The example below illustrates usage of a SQL
+database.
+
+```js
+var EthereumStrategy = require('passport-ethereum-siwe');
+var SessionNonceStore = require('passport-ethereum-siwe').SessionNonceStore;
+
+var store = new SessionChallengeStore();
+
+passport.use(new EthereumStrategy({ store: store }, function verify(address, cb) {
+  db.get('SELECT * FROM blockchain_credentials WHERE chain = ? AND address = ?', [
+    'eip155:1',
+    address
+  ], function(err, row) {
+    if (err) { return cb(err); }
+    if (!row) {
+      db.run('INSERT INTO users (username) VALUES (?)', [
+        address
+      ], function(err) {
+        if (err) { return cb(err); }
+        var id = this.lastID;
+        db.run('INSERT INTO blockchain_credentials (user_id, chain, address) VALUES (?, ?, ?)', [
+          id,
+          'eip155:1',
+          address
+        ], function(err) {
+          if (err) { return cb(err); }
+          var user = {
+            id: id,
+            username: address
+          };
+          return cb(null, user);
+        });
+      });
+    } else {
+      db.get('SELECT rowid AS id, * FROM users WHERE rowid = ?', [ row.user_id ], function(err, row) {
+        if (err) { return cb(err); }
+        if (!row) { return cb(null, false); }
+        return cb(null, row);
+      });
+    }
+  });
+}));
+```
+
+#### Define Routes
+
+Two routes are needed in order to allow users to log in with their Ethereum
+wallet.
+
+The first route generates a randomized challenge, saves it in the
+`ChallengeStore`, and sends it to the client-side JavaScript for it to be
+included in the signed message.  This is necessary in order to protect against
+replay attacks.
+
+```js
+router.post('/login/ethereum/challenge', function(req, res, next) {
+  store.challenge(req, function(err, nonce) {
+    if (err) { return next(err); }
+    res.json({ nonce: nonce });
+  });
+});
+```
+
+The second route authenticates the signed message and logs the user in.
+
+```js
+router.post('/login/ethereum',
+  passport.authenticate('ethereum', { failWithError: true }),
+  function(req, res, next) {
+    res.json({ ok: true });
+  },
+  function(err, req, res, next) {
+    res.json({ ok: false });
+  });
+```
+
+## Examples
+
+* [todos-express-ethereum](https://github.com/passport/todos-express-ethereum)
+
+  Illustrates how to use the Ethereum strategy within an Express application.
+
+## License
+
+[The MIT License](https://opensource.org/licenses/MIT)
+
+Copyright (c) 2022 Jared Hanson <[https://www.jaredhanson.me/](https://www.jaredhanson.me/)>