error: implement std's Error trait

src/core/error.rs

@@ -52,6 +52,21 @@ impl ResponseError for Error {
     }
 }
 
+impl std::error::Error for Error {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Error::BadToken(e) => Some(e),
+            Error::Crypto(e) => Some(e),
+            Error::Database(e) => Some(e),
+            Error::Invalid(e) => Some(e),
+            Error::Io(e) => Some(e),
+            Error::MalformedHeader(e) => Some(e),
+            Error::Reqwest(e) => Some(e),
+            _ => None,
+        }
+    }
+}
+
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {

src/util/crypto.rs

@@ -360,6 +360,12 @@ where
     }
 }
 
+impl std::error::Error for Error {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        self.0.source()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/util/validate.rs

@@ -158,3 +158,5 @@ impl fmt::Display for Error {
         Ok(())
     }
 }
+
+impl std::error::Error for Error {}