anchor.diff:  ```
   There is no requirement that this configuration option is a pattern, it can be a fixed URI value.
   
  -* `remoteIdpEntityId` - (required) the entity ID of the Identity Provider. Always a fixed URI value or string,
  -no patterns allowed.
   * `assertionConsumerServiceUrlTemplate` - (optional) A URI pattern that denotes the assertion
   consumer service URI to be sent with any `AuthNRequest` from the SP to the IDP during the SP initiated flow.
   While this can be a pattern the actual URI must resolve to the ACS endpoint on the SP.
   The default value is `+{baseUrl}/login/saml2/sso/{registrationId}+` and maps directly to the
   https://github.com/spring-projects/spring-security/blob/5.2.0.RELEASE/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/servlet/filter/Saml2WebSsoAuthenticationFilter.java#L42[`Saml2WebSsoAuthenticationFilter`] endpoint
  -* `idpWebSsoUrl`  - (required) a fixed URI value for the IDP Single Sign On endpoint where
  -the SP sends the `AuthNRequest` messages.
   * `credentials` - A list of credentials, private keys and x509 certificates, used for
   message signing, verification, encryption and decryption.
   This list can contain redundant credentials to allow for easy rotation of credentials.
  
positive.code: [[servlet-saml2-sp-initiated]]
  ==== Authentication Requests - SP Initiated Flow
  
  To initiate an authentication from the web application, a simple redirect to
  
  `+{baseUrl}/saml2/authenticate/{registrationId}+`
  
  The endpoint will generate an `AuthNRequest` by invoking the `createAuthenticationRequest` method on a
  configurable factory. Just expose the `Saml2AuthenticationRequestFactory` as a bean in your configuration.
  [source,java]
  ----
  public interface Saml2AuthenticationRequestFactory {
      String createAuthenticationRequest(Saml2AuthenticationRequest request);
  }
  ----
  
  
negative.code: ** [2] - PrivateKey/X509Certificate{SIGNING,DECRYPTION} - The SP's first signing and decryption credential.
  ** [3] - PrivateKey/X509Certificate{SIGNING,DECRYPTION} - The SP's second decryption credential.
  Signing is always done using the first `SIGNING` key in the list.
  * `ProviderDetails#entityId` - (required) the entity ID of the Identity Provider. Always a fixed URI value or string,
  no patterns allowed.
  * `ProviderDetails#webSsoUrl`  - (required) a fixed URI value for the IDP Single Sign On endpoint where
  the SP sends the `AuthNRequest` messages.
  * `ProviderDetails#signAuthNRequest` - A boolean indicating whether or not to sign the `AuthNRequest` with the SP's private key, defaults to `true`
  * `ProviderDetails#binding` - A `Saml2MessageBinding` indicating what kind of binding to use for the `AuthNRequest`, whether that be `REDIRECT` or `POST`, defaults to `REDIRECT`
  
  When an incoming message is received, signatures are always required, the system will first attempt
  to validate the signature using the certificate at index [0] and only move to the second
  