…(WouterJ)

This PR was squashed before being merged into the 2.8 branch (closes #15141).

Discussion
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[DX] [Security] Renamed Token#getKey() to getSecret()

There are 2 very vague parameter names in the authentication process: `$providerKey` and `$key`. Some tokens/providers have the first one, some tokens/providers the second one and some both. An overview:

| Token | `providerKey` | `key`
| --- | --- | ---
| `AnonymousToken` | - | yes
| `PreAuth...Token` | yes | -
| `RememberMeToken` | yes | yes
| `UsernamePasswordToken` | yes | -

Both names are extremely general and their PHPdocs contains pure no-shit-sherlock-descriptions :squirrel: (like "The key."). This made me and @iltar think it's just an inconsistency and they have the same meaning.
...until we dived deeper into the code and came to the conclusion that `$key` has a Security task (while `$providerKey` doesn't really). If it takes people connected to Symfony internals 30+ minutes to find this out, it should be considered for an improvement imo.

So here is our suggestion: **Rename `$key` to `$secret`**. This explains much better what the value of the string has to be (for instance, it's important that the string is not easily guessable and cannot be found out, according to the Spring docs). It also explains the usage better (it's used as a replacement for credentials and to hash the RememberMeToken).

**Tl;dr**: `$key` and `$providerKey` are too general names, let's improve DX by renaming them. This PR tackles `$key` by renaming it to `$secret`.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

*My excuse for the completely unrelated branch name*

Commits
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24e0eb6 [DX] [Security] Renamed Token#getKey() to getSecret()

This PR was merged into the 2.8 branch.

Discussion
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[DX] [Security] Renamed key to secret

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?  | yes symfony/symfony#15141
| Applies to    | 2.8+
| Fixed tickets | n/a

Commits
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18c7f04 Remember me, Renamed key to secret

…_me (stof)

This PR was merged into the 2.8 branch.

Discussion
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Fix the BC layer for the key->secret renaming for remember_me

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony/symfony-docs#5765
| License       | MIT
| Doc PR        | n/a

There was a mistake in #15141 removing the configuration entirely.

Commits
-------

f52b3a0 Fix the BC layer for the key->secret renaming for remember_me

…_me (stof)

This PR was merged into the 2.8 branch.

Discussion
----------

Fix the BC layer for the key->secret renaming for remember_me

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony/symfony-docs#5765
| License       | MIT
| Doc PR        | n/a

There was a mistake in symfony/symfony#15141 removing the configuration entirely.

Commits
-------

f52b3a0 Fix the BC layer for the key->secret renaming for remember_me

This PR was merged into the 2.8 branch.

Discussion
----------

[Security] Renamed key to secret Part 2

Anonymous and RememberMe were already changed in #15141 This PR renames 2 more occurences of key in the Security: AnonymousAuthenticationListener and the Digest entry point.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Commits
-------

55f59d5 Renamed key to secret