Add guide page

Author: frankie567

docs/guide.md

@@ -0,0 +1,105 @@
+# Guide
+
+This will guide you through the basic features of `pwdlib`.
+
+## Password hashing
+
+To manage password hashes, `pwdlib` exposes the [`PasswordHash`](./reference/pwdlib.md#pwdlib.PasswordHash) class. The difference with a "plain" hash algorithm helper is that it supports **multiple algorithms**. Why it's useful?
+
+Currently, the safest and recommended algorithm for password hashing is [Argon2](https://en.wikipedia.org/wiki/Argon2). But it's probable that in the coming years, a new and even safer algorithm emerges. Thanks to a wrapper like [`PasswordHash`](./reference/pwdlib.md#pwdlib.PasswordHash), we'll be able to verify hash generated with the older algorithm while upgrading them to the newer one.
+
+This is how you create an instance of [`PasswordHash`](./reference/pwdlib.md#pwdlib.PasswordHash) with Argon2 and Bcrypt support:
+
+```py
+from pwdlib import PasswordHash, exceptions
+from pwdlib.hashers.argon2 import Argon2Hasher
+from pwdlib.hashers.bcrypt import BcryptHasher
+
+password_hash = PasswordHash((
+    Argon2Hasher(),
+    BcryptHasher(),
+))
+```
+
+[`PasswordHash`](./reference/pwdlib.md#pwdlib.PasswordHash) expects a tuple (or list) of hashing algorithms.
+
+!!! warning "The corresponding dependencies must be installed"
+
+    Hashing algorithms are available through third-party implementations. Therefore, you should install the extra for all the algorithms you want to use.
+
+    **For Argon2**
+
+    ```sh
+    pip install 'pwdlib[argon2]'
+    ```
+
+    **For Bcrypt**
+
+    ```sh
+    pip install 'pwdlib[bcrypt]'
+    ```
+
+    **Both!**
+
+    ```sh
+    pip install 'pwdlib[argon2,bcrypt]'
+    ```
+
+The **first** algorithm in the list is considered the **current algorithm**. New and updated hashes will use this algorithm.
+
+!!! tip "I don't know what to choose!"
+
+    If you start a new application, you can instantiate [`PasswordHash`](./reference/pwdlib.md#pwdlib.PasswordHash) using the [`recommended`](./reference/pwdlib.md#pwdlib.PasswordHash.recommended) class method. It'll use the Argon2 algorithm under the hood.
+
+    ```py
+    password_hash = PasswordHash.recommended()
+    ```
+
+### Hash a password
+
+Once you have a [`PasswordHash`](./reference/pwdlib.md#pwdlib.PasswordHash) instance, you can [`hash`](./reference/pwdlib.md#pwdlib.PasswordHash.hash) a user's password:
+
+```py
+hash = password_hash.hash("herminetincture")
+```
+
+The resulting string is a hash generated from the **current algorithm**, which you can safely store in your database.
+
+!!! question "Where is the salt?"
+
+    If you know about password hashing algorithms, you probably know that *salting* the password is an important security feature. Back in the days, it was common to store the salt separately from the hash. Nowadays, most algorithms have a specific structure allowing them to store algorithm parameters and salt along with the hash in one string.
+
+    For example, here is an Argon2 hash:
+
+    ```
+    $argon2id$v=19$m=65536,t=3,p=4$ugY9gvgMUycvF7hrnoi8oQ$uqcZOh96YysaG+s3A+RcZIccgaiQsynxfBlqUNxeRT4
+    ```
+
+### Verify a password
+
+When you want to verify a password corresponds to a hash, use the [`verify`](./reference/pwdlib.md#pwdlib.PasswordHash.verify) method:
+
+```py
+valid = password_hash.verify(hash, "herminetincture")
+```
+
+Under the hood, it'll check against all the enabled algorithms. It means that if older users still have a hash with a legacy algorithm, we'll still be able to verify it.
+
+The resulting boolean indicates you if the hash corresponds to this password or not.
+
+However, in most cases, you probably want to use the method we describe below.
+
+### Verify and update a password
+
+As we said, [`verify`](./reference/pwdlib.md#pwdlib.PasswordHash.verify) checks the hash against all the enabled algorithms. However, it's generally a good idea to take this chance to update the hash to the more secure current algorithm.
+
+This is the purpose of the [`verify_and_update`](./reference/pwdlib.md#pwdlib.PasswordHash.verify_and_update) method: it verifies the password against a hash and, if it's valid and using an outdated algorithm, will hash it again using the current algorithm.
+
+
+```py
+valid, updated_hash = password_hash.verify_and_update(hash, "herminetincture")
+```
+
+If the hash needs to be updated, `updated_hash` will be a string. Otherwise, it's `None`. Then, don't forget to update it in your database.
+
+It's worth to note that the hash is also upgraded if the **settings of the algorithm** has been changed, like the time or memory cost.

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 nav:
     - About: index.md
+    - Guide: guide.md
     - Reference:
         - pwdlib: reference/pwdlib.md
         - pwdlib.exceptions: reference/pwdlib.exceptions.md