Spring Security SAML - Signing Algorithm - spring

Question

I'm pretty new to SAML 2.0 but got tasked with integrating it into our existing webapplication using Spring Security 4.2.2 and Spring Security Saml2 1.0.2.
Our initial tests went fine when using Okta as IdP.
One customer however is unable to process the SAMLRequest in the redirect because the signing algorithm defaults to http://www.w3.org/2000/09/xmldsig#dsa-sha1 which they do not support.
So I need to change this to something that they do support (for example RSA-SHA256).
How can I change the signing algorithm that is used when forwarding to the IdP?
All help greatly appreciated!
I already tried changing the signingAlgorithm property of the defaultMetadata in my metadataGeneratorFilter but that didn't change anything to the SAMLRequest:
<bean id="metadataGeneratorFilter" class="org.springframework.security.saml.metadata.MetadataGeneratorFilter">
<constructor-arg>
<bean class="org.springframework.security.saml.metadata.MetadataGenerator">
<property name="entityBaseURL" value="..." />
<property name="extendedMetadata">
<bean class="org.springframework.security.saml.metadata.ExtendedMetadata">
<property name="signingAlgorithm" value="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256" />
</bean>
</property>
</bean>
</constructor-arg>
</bean>
UPDATE 1: I discovered that the keystore we were using had the signing algorithm set to DSA so I generated a new keystore with the correct parameters
keytool -genkeypair -alias saml -keypass <password> -keystore saml.jks -keyalg RSA -sigalg SHA256withRSA
This accomplished that the SigAlg parameter was now set to RSA_SHA1 (even though my keystore uses RSA_SHA256 but more on that in UPDATE2)
UPDATE 2: it appears that OpenSaml, more specifically xmltooling, defaults to RSA_SHA1. I found a workaround here: https://myshittycode.com/2016/02/23/spring-security-saml-replacing-sha-1-with-sha-256-on-signature-and-digest-algorithms/
Now my implementation is happily using RSA_SHA256 (yay)
I'm still going to see if we can accomplish the same thing without a custom bootstrap class but at least everything is working right now.