algorithms: expose AlgorithmFamily

It is available on `DecodingKey`. Since `Validation` ends up masking out
keys based on a single family, allow crates to create a list of
supported algorithms based on the family in use.

See: #297

Author: mathstuf

src/algorithms.rs

@@ -4,6 +4,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::errors::{Error, ErrorKind, Result};
 
+/// Supported families of algorithms.
 #[derive(Debug, Eq, PartialEq, Copy, Clone, Serialize, Deserialize)]
 pub enum AlgorithmFamily {
     Hmac,
@@ -88,7 +89,7 @@ impl FromStr for Algorithm {
 }
 
 impl Algorithm {
-    pub(crate) fn family(self) -> AlgorithmFamily {
+    pub fn family(self) -> AlgorithmFamily {
         match self {
             Algorithm::HS256 | Algorithm::HS384 | Algorithm::HS512 => AlgorithmFamily::Hmac,
             Algorithm::RS256

src/lib.rs

@@ -13,7 +13,7 @@ compile_error!(
 #[cfg(not(any(feature = "rust_crypto", feature = "aws_lc_rs")))]
 compile_error!("at least one of the features \"rust_crypto\" or \"aws_lc_rs\" must be enabled");
 
-pub use algorithms::Algorithm;
+pub use algorithms::{Algorithm, AlgorithmFamily};
 pub use decoding::{DecodingKey, TokenData, decode, decode_header};
 pub use encoding::{EncodingKey, encode};
 pub use header::Header;