Create X509 certificate from base64 CSR string and CA root certificate in c#

Question

I need to generate a certificate starting from the base64 string value of a PEM encoded CSR and a CA root certificate.

The CA certificate is generated using openssl from the command line.

Given that CertificateRequest api from .NET does not provide a .FromPemBase64String() method, it is basically impossible to use it in my case. I have tried to find a solution using BouncyCastle library but most of the solutions I have found generate a CSR on the fly while I actually need it to be parsed from a string.

Currently my solution is to:

store the CSR to a file (test.csr)
programmatically run the following command: openssl x509 -req -in test.csr -CA ca.crt -CAkey ca.key -passin pass:"password123" -CAcreateserial -out test.crt -days 730 -sha256

Everything works fine but it would be great if I can find a programmatically way to do the same (including generating the CA on the fly so I don't have to add the files to the project).

Does anyone have any suggestions?

I am currently using .NET6

You should use a specialized CA software. Generating certificates from the code never was a good idea. — Crypt32, Jul 19 '22 at 13:12
Very helpful! thank you so much @bartonjs. BTW Crypt32 I just need to do this in an integration test to test some business logic. I won't create certificates using custom CA in production — Mauro.Franchi, Jul 19 '22 at 17:00

Create X509 certificate from base64 CSR string and CA root certificate in c#

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