Troubleshooting 431 Status Code When Creating a SAMLAssertion Destination in SAP BTP

[Shubham_Savani]

Issue Overview:

I’m facing an issue while setting up a SAMLAssertion destination in SAP BTP. I’m encountering a 431 status code when checking the connection for the destination. The 431 status code stands for "Request Header Fields Too Large". This error indicates that the request headers being sent to the server are exceeding its size limits. In my case, this is happening while using SAMLAssertion as the authentication method for an SAP destination.

From what I understand, SAML tokens can sometimes become quite large, and this can cause issues when they are passed in the request headers. However, I’m not sure how to proceed in resolving the issue.

Details of the Issue:

• Setup: SAMLAssertion-based authentication for an SAP destination.
• Error: When I attempt to check the connection, I receive a 431 status code.
• Potential Cause: The error might be related to the size of the SAML token or other header fields being sent as part of the request. However, I haven’t been able to identify the exact cause or find a solution.

Seeking Suggestions:

I’ve done some research, but I haven’t come across a definitive solution yet. I’m reaching out to the community to see if anyone has encountered a similar problem and managed to resolve it.

• Has anyone faced this issue with SAMLAssertion destinations?
• What are some potential ways to reduce the header size in such cases?
• Could the issue be related to proxy or gateway limits? If so, what adjustments helped?

Any advice or suggestions would be greatly appreciated!

Destination

Fiori Genrator

Conclusion:

Dealing with a 431 status code while using SAMLAssertion in SAP is proving to be quite a challenge. I’d love to hear from anyone who has tackled this issue or has insights into potential solutions.

[gregorw]

Can you provide details what backend system you try to call? I think you would need to get in touch with the admin of this system to increase the header limit. Or you need to shrink your BTP token to get a smaller SAML Assertion.

[Shubham_Savani]

Hi, thanks for the prompt response!

I am using Cloud foundry environment and nodejs in BAS, SAP hana cloud for db. How should I proceed for this?

Regards,
Shubham

[gregorw]

Let us know what the backend is that you connect to via this SAMLAssertion destination.

[Shubham_Savani]

I am using SAP HANA Cloud for db and I am using CAPM for the backend system.

[gregorw]

In a CAP application you don't connect to HANA via a destination. You use a service binding.

[Shubham_Savani]

I have created a backend system using CAPM and now I want to connect this system to Frontend system using destination and for this I want to use SAMLAssertion mechanism for security. While doing so I am encountering 431 error while checking connection in destination. What configuration do I have to implement in BAS to achieve this? 

[gregorw]

Is the frontend part of the project you've created the CAP Application in? Do you use the standalone or managed approuter?

[gregorw]

Where have you found information that SAMLAssertion would be the correct way to authenticate?

[Shubham_Savani]

No the frontend part is in different bas space, I have used xsuaa in pacakge.json to use Oauth2ClientCredentials mechanism but it is only working in full stack case not when fortend and backend are in different spaces. In this I have used managed Approuter. There are other protocols mentioned in the destination and in neo I have used SAML so I wanted to use SAMLAssertion in the same way here.

[gregorw]

Do you use the same XSUAA instance for backend and frontend?

[WouterLemaire]

Hi,

We faced the same issue and applied the suggestion of Gregor by making the saml assertion token smaller. We achieved this  by limiting the user groups or ad groups in the saml ticket depending on the connected system. We provide a unique identifier to the company idp that will be used to only return a subset of ad groups instead of all.

[Shubham_Savani]

Hi, thanks for the prompt response!

I have done "xsuaa":"mocked" in package.json and hence my xs-security.json is empty. I have no assigned groups in it so how should I reduce the size of the header?

Regards,
Shubham