fix(sdk): narrow SRT signer exceptions

Signed-off-by: strantalis <strantalis@virtru.com>

Author: strantalis

sdk/src/main/java/io/opentdf/platform/sdk/DefaultSrtSigner.java

@@ -19,8 +19,12 @@ final class DefaultSrtSigner implements SrtSigner {
     }
 
     @Override
-    public byte[] sign(byte[] input) throws Exception {
-        return signer.sign(HEADER, input).decode();
+    public byte[] sign(byte[] input) throws java.security.GeneralSecurityException {
+        try {
+            return signer.sign(HEADER, input).decode();
+        } catch (JOSEException e) {
+            throw new java.security.GeneralSecurityException("error signing SRT payload", e);
+        }
     }
 
     @Override

sdk/src/main/java/io/opentdf/platform/sdk/KASClient.java

@@ -219,7 +219,7 @@ public Base64URL sign(JWSHeader header, byte[] signingInput) throws JOSEExceptio
 
             try {
                 return Base64URL.encode(srtSigner.sign(signingInput));
-            } catch (Exception e) {
+            } catch (java.security.GeneralSecurityException e) {
                 throw new JOSEException("error signing SRT payload", e);
             }
         }

sdk/src/main/java/io/opentdf/platform/sdk/SrtSigner.java

@@ -1,7 +1,7 @@
 package io.opentdf.platform.sdk;
 
 public interface SrtSigner {
-    byte[] sign(byte[] input) throws Exception;
+    byte[] sign(byte[] input) throws java.security.GeneralSecurityException;
 
     String alg();
 }

sdk/src/test/java/io/opentdf/platform/sdk/KASClientTest.java

@@ -205,7 +205,7 @@ public byte[] sign(byte[] input) {
                             .sign(new JWSHeader.Builder(JWSAlgorithm.RS256).build(), input)
                             .decode();
                 } catch (JOSEException e) {
-                    throw new RuntimeException(e);
+                    throw new AssertionError("Signing failed unexpectedly in test", e);
                 }
             }