Change default keyval state file location. (#90)

Previously, the keyval state file was configured to be stored in the "conf.d"
directory. By default, the NGINX process does not have write access to this
directory, necessitating users to either specify a different path or alter
the directory permissions.

The default path for the state file has been changed to "/var/lib/nginx/state".
This new location is more suitable for most Linux users and aligns with
security best practices, as only the NGINX user has read and write permissions
by default.

Author: route443

README.md

@@ -136,9 +136,9 @@ Manual configuration involves reviewing the following files so that they match y
 The key-value store is used to maintain persistent storage for ID tokens and refresh tokens. The default configuration should be reviewed so that it suits the environment. This is part of the advanced configuration in **openid_connect_configuration.conf**.
 
 ```nginx
-keyval_zone zone=oidc_id_tokens:1M     state=conf.d/oidc_id_tokens.json     timeout=1h;
-keyval_zone zone=oidc_access_tokens:1M state=conf.d/oidc_access_tokens.json timeout=1h;
-keyval_zone zone=refresh_tokens:1M     state=conf.d/refresh_tokens.json     timeout=8h;
+keyval_zone zone=oidc_id_tokens:1M     state=/var/lib/nginx/state/oidc_id_tokens.json     timeout=1h;
+keyval_zone zone=oidc_access_tokens:1M state=/var/lib/nginx/state/oidc_access_tokens.json timeout=1h;
+keyval_zone zone=refresh_tokens:1M     state=/var/lib/nginx/state/refresh_tokens.json     timeout=8h;
 keyval_zone zone=oidc_pkce:128K timeout=90s;
 ```
 

openid_connect_configuration.conf

@@ -87,9 +87,9 @@ map $http_x_forwarded_proto $proto {
 proxy_cache_path /var/cache/nginx/jwk levels=1 keys_zone=jwk:64k max_size=1m;
 
 # Change timeout values to at least the validity period of each token type
-keyval_zone zone=oidc_id_tokens:1M     state=conf.d/oidc_id_tokens.json     timeout=1h;
-keyval_zone zone=oidc_access_tokens:1M state=conf.d/oidc_access_tokens.json timeout=1h;
-keyval_zone zone=refresh_tokens:1M     state=conf.d/refresh_tokens.json     timeout=8h;
+keyval_zone zone=oidc_id_tokens:1M     state=/var/lib/nginx/state/oidc_id_tokens.json     timeout=1h;
+keyval_zone zone=oidc_access_tokens:1M state=/var/lib/nginx/state/oidc_access_tokens.json timeout=1h;
+keyval_zone zone=refresh_tokens:1M     state=/var/lib/nginx/state/refresh_tokens.json     timeout=8h;
 keyval_zone zone=oidc_pkce:128K timeout=90s; # Temporary storage for PKCE code verifier.
 
 keyval $cookie_auth_token $session_jwt   zone=oidc_id_tokens;     # Exchange cookie for JWT