feature #4369 [reference][configuration][security]Added key_length for pbkdf2 encoder (Guillaume-Rossignol)

This PR was merged into the 2.3 branch.

Discussion
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[reference][configuration][security]Added key_length for pbkdf2 encoder

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | >=2.2
| Fixed tickets | -

Commits
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730dbb8 [Config] Complete security encoder in full default configuration
4b9a885 [reference][configuration][security]Added key_length for pbkdf2 encoder

Author: weaverryan

reference/configuration/security.rst

@@ -62,11 +62,24 @@ Each part will be explained in the next section.
                     hash_algorithm:       sha512
                     encode_as_base64:     true
                     iterations:           1000
+                    key_length:           40
 
                 # Example options/values for what a custom encoder might look like
                 Acme\DemoBundle\Entity\User3:
                     id:                   my.encoder.id
 
+                # BCrypt encoder
+                # see the note about bcrypt below for details on specific dependencies
+                Acme\DemoBundle\Entity\User4:
+                    algorithm:            bcrypt
+                    cost:                 13
+
+                # Plaintext encoder
+                # it does not do any encoding
+                Acme\DemoBundle\Entity\User5:
+                    algorithm:            plaintext
+                    ignore_case:          false
+
             providers:            # Required
                 # Examples:
                 my_in_memory_provider: