src/main/java/de/mlessmann/certassist/web/CertificatesEndpoint.java

@@ -5,20 +5,27 @@ import de.mlessmann.certassist.models.CertificateInfo;
 import de.mlessmann.certassist.models.CertificateInfoSubject;
 import de.mlessmann.certassist.repositories.CertificateRepository;
 import de.mlessmann.certassist.service.CertificateCreationService;
+import de.mlessmann.certassist.web.dto.PrivateKey;
 import io.swagger.v3.oas.annotations.Operation;
+import io.swagger.v3.oas.annotations.media.Content;
+import io.swagger.v3.oas.annotations.media.Schema;
 import io.swagger.v3.oas.annotations.responses.ApiResponse;
 import lombok.RequiredArgsConstructor;
 import org.springdoc.core.annotations.ParameterObject;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.data.domain.Pageable;
 import org.springframework.http.ResponseEntity;
+import org.springframework.util.MimeTypeUtils;
 import org.springframework.web.bind.annotation.*;
 
+import java.nio.charset.StandardCharsets;
+
 @RestController
 @RequestMapping("/api")
 @RequiredArgsConstructor(onConstructor_ = @Autowired)
 public class CertificatesEndpoint {
 
+    public static final String MIME_PEM_FILE = "application/x-pem-file";
     private final CertificateRepository certificateRepository;
     private final CertificateCreationService certificateCreationService;
 
@@ -48,4 +55,34 @@ public class CertificatesEndpoint {
         return ResponseEntity.ok(createdCertificate);
     }
 
+    @GetMapping(value = "/certificates/{cert}/privateKey", produces = {
+            MimeTypeUtils.APPLICATION_JSON_VALUE,
+            MIME_PEM_FILE
+    })
+    @Operation(description = "Fetches the private key corresponding to the provided certificate.",
+            responses = {
+                    @ApiResponse(responseCode = "200", content = {
+                            @Content(mediaType = MimeTypeUtils.APPLICATION_JSON_VALUE,
+                                    schema = @Schema(implementation = PrivateKey.class)),
+                            @Content(mediaType = MIME_PEM_FILE,
+                                    schema = @Schema(type = "string", description = "PEM formatted private key content"))
+                    })
+            })
+    public ResponseEntity<Object> getCertificatePrivateKey(
+            @RequestHeader("Accept") String acceptType,
+            @PathVariable String cert
+    ) {
+        var requestedCert = certificateRepository.findByFingerprintIs(cert);
+
+        if (MimeTypeUtils.APPLICATION_JSON_VALUE.equals(acceptType)) {
+            String pemContent = new String(requestedCert.getPrivateKey(), StandardCharsets.UTF_8);
+            var pKey = new PrivateKey(pemContent);
+            return ResponseEntity.ok(pKey);
+        } else if (MIME_PEM_FILE.equals(acceptType)) {
+            String pemContent = new String(requestedCert.getPrivateKey(), StandardCharsets.UTF_8);
+            return ResponseEntity.ok(pemContent);
+        } else {
+            return ResponseEntity.badRequest().build();
+        }
+    }
 }

src/main/java/de/mlessmann/certassist/web/dto/PrivateKey.java

@@ -0,0 +1,11 @@
+package de.mlessmann.certassist.web.dto;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import io.swagger.v3.oas.annotations.media.Schema;
+
+@Schema(description = "Represents the private key of a certificate.")
+public record PrivateKey(
+        @JsonProperty
+        @Schema(description = "The content of the private key as it would be in a .pem file.")
+        String pemContent) {
+}