Add support to obtain PEM-encoded certificates as X509Certificate

[abremora]

Certificate.getX509Certificate() and Certificate.getX509IssuerCertificate() do not support conversion of PEM-encoded string to X509Certificate.

[abremora]

It's odd in that the default of the returned data is PEM.

format (string: "") – Specifies the format for returned data. Can be pem, der, or pem_bundle; defaults to pem.
If der, the output is base64 encoded. If pem_bundle, the certificate field will contain the private key and certificate,
concatenated; if the issuing CA is not a Vault-derived self-signed root, this will be included as well.

https://www.vaultproject.io/api-docs/secret/pki#generate-certificate

[mp911de]

As per the documentation:

spring-vault/spring-vault-core/src/main/java/org/springframework/vault/support/Certificate.java

Lines 32 to 33 in 2e02491

	* certificate. Certificate and keys can be either DER or PEM encoded. DER-encoded
	* certificates can be converted to a {@link X509Certificate}.

Feel free to submit a pull request to introduce PEM to X509Certificate decoding.

[abremora]

Same issue affects CertificateBundle.createKeyStore() & CertificateBundle.getPrivateKeySpec(), too. (Already mentioned in the documentation)

java.lang.IllegalArgumentException: Illegal base64 character 2d
	at java.base/java.util.Base64$Decoder.decode0(Base64.java:746) ~[na:na]
	at java.base/java.util.Base64$Decoder.decode(Base64.java:538) ~[na:na]
	at org.springframework.util.Base64Utils.decode(Base64Utils.java:59) ~[spring-core-5.3.13.jar:5.3.13]
	at org.springframework.util.Base64Utils.decodeFromString(Base64Utils.java:111) ~[spring-core-5.3.13.jar:5.3.13]
	at org.springframework.vault.support.CertificateBundle.getPrivateKeySpec(CertificateBundle.java:89) ~[spring-vault-core-2.3.2.jar:2.3.2]
	at org.springframework.vault.support.CertificateBundle.createKeyStore(CertificateBundle.java:109) ~[spring-vault-core-2.3.2.jar:2.3.2]

[abremora]

Just for clarification: For Vault the default is PEM but for spring-vault the default is DER:

spring-vault/spring-vault-core/src/main/java/org/springframework/vault/core/VaultPkiTemplate.java

Line 91 in 26a77a2

request.put("format", "der");

I will fix this issue within the next days.

[abremora]

Of course we cannot change the behavior of vault-spring but we have to support other formats and improve documentation.