commit 97420d1930c4c7cd6b5701f5c5a3a09bfbd17b93 · bretton.dev/coves

+52

internal/atproto/auth/combined_key_fetcher.go

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       package auth

     

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       import (

     

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       	"context"

     

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       	"fmt"

     

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       	"strings"

     

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       	indigoIdentity "github.com/bluesky-social/indigo/atproto/identity"

     

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       )

     

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       // CombinedKeyFetcher handles JWT public key fetching for both:

     

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       // - DID issuers (did:plc:, did:web:) → resolves via DID document

     

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       // - URL issuers (https://) → fetches via JWKS endpoint (legacy/fallback)

     

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       //

     

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       // For atproto service authentication, the issuer is typically the user's DID,

     

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       // and the signing key is published in their DID document.

     

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       type CombinedKeyFetcher struct {

     

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       	didFetcher  *DIDKeyFetcher

     

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       	jwksFetcher JWKSFetcher

     

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       }

     

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       // NewCombinedKeyFetcher creates a key fetcher that supports both DID and URL issuers.

     

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       // Parameters:

     

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       //   - directory: Indigo's identity directory for DID resolution

     

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       //   - jwksFetcher: fallback JWKS fetcher for URL issuers (can be nil if not needed)

     

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       func NewCombinedKeyFetcher(directory indigoIdentity.Directory, jwksFetcher JWKSFetcher) *CombinedKeyFetcher {

     

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       	return &CombinedKeyFetcher{

     

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       		didFetcher:  NewDIDKeyFetcher(directory),

     

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       		jwksFetcher: jwksFetcher,

     

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       	}

     

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       }

     

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       // FetchPublicKey fetches the public key for verifying a JWT.

     

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       // Routes to the appropriate fetcher based on issuer format:

     

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       // - DID (did:plc:, did:web:) → DIDKeyFetcher

     

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       // - URL (https://) → JWKSFetcher

     

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       func (f *CombinedKeyFetcher) FetchPublicKey(ctx context.Context, issuer, token string) (interface{}, error) {

     

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       	// Check if issuer is a DID

     

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       	if strings.HasPrefix(issuer, "did:") {

     

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       		return f.didFetcher.FetchPublicKey(ctx, issuer, token)

     

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       	}

     

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       	// Check if issuer is a URL (https:// or http:// in dev)

     

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       	if strings.HasPrefix(issuer, "https://") || strings.HasPrefix(issuer, "http://") {

     

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       		if f.jwksFetcher == nil {

     

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       			return nil, fmt.Errorf("URL issuer %s requires JWKS fetcher, but none configured", issuer)

     

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       		}

     

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       		return f.jwksFetcher.FetchPublicKey(ctx, issuer, token)

     

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       	}

     

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       	return nil, fmt.Errorf("unsupported issuer format: %s (expected DID or URL)", issuer)

     

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       }

+116

internal/atproto/auth/did_key_fetcher.go

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       package auth

     

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       import (

     

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       	"context"

     

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       	"crypto/ecdsa"

     

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       	"crypto/elliptic"

     

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       	"encoding/base64"

     

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       	"fmt"

     

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       	"math/big"

     

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       	"strings"

     

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       	"github.com/bluesky-social/indigo/atproto/atcrypto"

     

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       	indigoIdentity "github.com/bluesky-social/indigo/atproto/identity"

     

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       	"github.com/bluesky-social/indigo/atproto/syntax"

     

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       )

     

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       // DIDKeyFetcher fetches public keys from DID documents for JWT verification.

     

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       // This is the primary method for atproto service authentication, where:

     

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       // - The JWT issuer is the user's DID (e.g., did:plc:abc123)

     

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       // - The signing key is published in the user's DID document

     

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       // - Verification happens by resolving the DID and checking the signature

     

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       type DIDKeyFetcher struct {

     

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       	directory indigoIdentity.Directory

     

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       }

     

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       // NewDIDKeyFetcher creates a new DID-based key fetcher.

     

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       func NewDIDKeyFetcher(directory indigoIdentity.Directory) *DIDKeyFetcher {

     

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       	return &DIDKeyFetcher{

     

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       		directory: directory,

     

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       	}

     

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       }

     

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       // FetchPublicKey fetches the public key for verifying a JWT from the issuer's DID document.

     

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       // For DID issuers (did:plc: or did:web:), resolves the DID and extracts the signing key.

     

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       // Returns an *ecdsa.PublicKey suitable for use with jwt-go.

     

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       func (f *DIDKeyFetcher) FetchPublicKey(ctx context.Context, issuer, token string) (interface{}, error) {

     

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       	// Only handle DID issuers

     

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       	if !strings.HasPrefix(issuer, "did:") {

     

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       		return nil, fmt.Errorf("DIDKeyFetcher only handles DID issuers, got: %s", issuer)

     

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       	}

     

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       	// Parse the DID

     

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       	did, err := syntax.ParseDID(issuer)

     

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       	if err != nil {

     

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       		return nil, fmt.Errorf("invalid DID format: %w", err)

     

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       	}

     

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       	// Resolve the DID to get the identity (includes public keys)

     

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       	ident, err := f.directory.LookupDID(ctx, did)

     

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       	if err != nil {

     

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       		return nil, fmt.Errorf("failed to resolve DID %s: %w", issuer, err)

     

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       	}

     

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       	// Get the atproto signing key from the DID document

     

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       	pubKey, err := ident.PublicKey()

     

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       	if err != nil {

     

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       		return nil, fmt.Errorf("failed to get public key from DID document: %w", err)

     

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       	}

     

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       	// Convert to JWK format to extract coordinates

     

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       	jwk, err := pubKey.JWK()

     

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       	if err != nil {

     

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       		return nil, fmt.Errorf("failed to convert public key to JWK: %w", err)

     

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       	}

     

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       	// Convert atcrypto JWK to Go ecdsa.PublicKey

     

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       	return atcryptoJWKToECDSA(jwk)

     

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       }

     

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       // atcryptoJWKToECDSA converts an atcrypto.JWK to a Go ecdsa.PublicKey

     

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       func atcryptoJWKToECDSA(jwk *atcrypto.JWK) (*ecdsa.PublicKey, error) {

     

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       	if jwk.KeyType != "EC" {

     

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       		return nil, fmt.Errorf("unsupported JWK key type: %s (expected EC)", jwk.KeyType)

     

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       	}

     

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       	// Decode X and Y coordinates (base64url, no padding)

     

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       	xBytes, err := base64.RawURLEncoding.DecodeString(jwk.X)

     

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       	if err != nil {

     

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       		return nil, fmt.Errorf("invalid JWK X coordinate encoding: %w", err)

     

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       	}

     

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       	yBytes, err := base64.RawURLEncoding.DecodeString(jwk.Y)

     

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       	if err != nil {

     

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       		return nil, fmt.Errorf("invalid JWK Y coordinate encoding: %w", err)

     

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       	}

     

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       	var ecCurve elliptic.Curve

     

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       	switch jwk.Curve {

     

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       	case "P-256":

     

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       		ecCurve = elliptic.P256()

     

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       	case "P-384":

     

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       		ecCurve = elliptic.P384()

     

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       	case "P-521":

     

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       		ecCurve = elliptic.P521()

     

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       	case "secp256k1":

     

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       		// secp256k1 (K-256) is used by some atproto implementations

     

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       		// Go's standard library doesn't include secp256k1, but we can still

     

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       		// construct the key - jwt-go may not support it directly

     

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       		return nil, fmt.Errorf("secp256k1 curve requires special handling for JWT verification")

     

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       	default:

     

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       		return nil, fmt.Errorf("unsupported JWK curve: %s", jwk.Curve)

     

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       	}

     

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       	// Create the public key

     

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       	pubKey := &ecdsa.PublicKey{

     

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       		Curve: ecCurve,

     

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       		X:     new(big.Int).SetBytes(xBytes),

     

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       		Y:     new(big.Int).SetBytes(yBytes),

     

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       	}

     

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       	// Validate point is on curve

     

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       	if !ecCurve.IsOnCurve(pubKey.X, pubKey.Y) {

     

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       		return nil, fmt.Errorf("invalid public key: point not on curve")

     

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       	}

     

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       	return pubKey, nil

     

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       }