Add example for setting up client credentials

Closes gh-15304

Author: sjohnr

docs/modules/ROOT/pages/reactive/oauth2/index.adoc

@@ -69,8 +69,8 @@ See xref:getting-spring-security.adoc[] for additional options when not using Sp
 
 Consider the following use cases for OAuth2 Resource Server:
 
-* <<oauth2-resource-server-access-token,I want to protect access to the API using OAuth2>> (authorization server provides JWT or opaque access token)
-* <<oauth2-resource-server-custom-jwt,I want to protect access to the API using a JWT>> (custom token)
+* I want to <<oauth2-resource-server-access-token,protect access to the API using OAuth2>> (authorization server provides JWT or opaque access token)
+* I want to <<oauth2-resource-server-custom-jwt,protect access to the API using a JWT>> (custom token)
 
 [[oauth2-resource-server-access-token]]
 === Protect Access with an OAuth2 Access Token
@@ -393,13 +393,13 @@ See xref:getting-spring-security.adoc[] for additional options when not using Sp
 
 Consider the following use cases for OAuth2 Client:
 
-* <<oauth2-client-log-users-in,I want to log users in using OAuth 2.0 or OpenID Connect 1.0>>
-* <<oauth2-client-access-protected-resources,I want to obtain an access token for users in order to access a third-party API>>
-* <<oauth2-client-access-protected-resources-current-user,I want to do both>> (log users in _and_ access a third-party API)
-* <<oauth2-client-enable-extension-grant-type,I want to enable an extension grant type>>
-* <<oauth2-client-customize-existing-grant-type,I want to customize an existing grant type>>
-* <<oauth2-client-customize-request-parameters,I want to customize token request parameters>>
-* <<oauth2-client-customize-web-client,I want to customize the `WebClient` used by OAuth2 Client components>>
+* I want to <<oauth2-client-log-users-in,log users in using OAuth 2.0 or OpenID Connect 1.0>>
+* I want to <<oauth2-client-access-protected-resources,obtain an access token for users>> in order to access a third-party API
+* I want to <<oauth2-client-access-protected-resources-current-user,do both>> (log users in _and_ access a third-party API)
+* I want to <<oauth2-client-enable-extension-grant-type,enable an extension grant type>>
+* I want to <<oauth2-client-customize-existing-grant-type,customize an existing grant type>>
+* I want to <<oauth2-client-customize-request-parameters,customize token request parameters>>
+* I want to <<oauth2-client-customize-web-client,customize the `WebClient` used by OAuth2 Client components>>
 
 [[oauth2-client-log-users-in]]
 === Log Users In with OAuth2