erlang google oauth2 protocol for google calling apis - oauth-2.0

Question

Hello I am writing oauth 2 library to access google api's and my code is as follows
jwt_create() ->
{ok,PemBin} = file:read_file("your-key-file.pem"),
PemEntry = public_key:pem_decode(PemBin),
[A,B] = PemEntry,
io:format("A:: ~p ~n",[A]),
PrivateKey = public_key:pem_entry_decode(PemEntry),
JwtHeaderJson = encode_json(jwt_header()),
JwtClaimsetJson = encode_json(jwt_claimset()),
ComputeSignature = compute_signature(JwtHeaderJson, JwtClaimsetJson, PrivateKey),
Z=binary:replace(
binary:replace(<<JwtHeaderJson/binary, ".", JwtClaimsetJson/binary, ".", ComputeSignature/binary>>,
<<"+">>, <<"-">>, [global]),
<<"/">>, <<"_">>, [global]),
io:format("JWT:: ~p ~n",[Z]).
compute_signature(Header, ClaimSet,#'RSAPrivateKey'{publicExponent=Exponent
,modulus=Modulus
,privateExponent=PrivateExponent}) ->
base64:encode(crypto:sign(rsa, sha256, <<Header/binary, ".", ClaimSet/binary>>,
[Exponent, Modulus, PrivateExponent])).
encode_json(JWToken) ->
base64:encode(jsx:encode(JWToken)).
I am getting error as follows:
exception error: no function clause matching
public_key:pem_entry_decode([{'PrivateKeyInfo',<<48,130,4,191,2,1,0,48,13,6,9,42,134,
72,134,247,13,1,1,1,5,0,4,130,4,...>>,
not_encrypted},
{'Certificate',<<48,130,3,96,48,130,2,72,160,3,2,1,2,2,8,
79,59,244,35,60,15,3,155,48,...>>,
not_encrypted}]) (public_key.erl, line 123)
in function googleoauth:jwt_create/0 (src/googleoauth.erl, line 55)
Please help me in generating JWS and JWT for OAUTH 2 for accessing google apis

Answer 1

You are passing the wrong thing to public_key:pem_entry_decode/1:
This will resolve your problem:
PrivateKey = public_key:pem_entry_decode(A),
public_key:pem_entry_decode/1 takes a single pem_entry() but a PEM file can contain many entries, perhaps your code PemEntry = public_key:pem_decode(PemBin) should read PemEntries = public_key:pem_decode(PemBin) instead?
Also note the line before assumes 2 list entries, you might have meant this instead (not sure your intent here though)?
[A|B] = PemEntry,